Thought it might be interesting to share, so below it goes.

Feel free to suggest any more!

RSS search/lookup tools
  • RSSHub Radar - browser extension that tries to find RSS links in pages currently being looked at.
  • RSS Lookup - the site looks up for feeds in the page that loads by the link the user provides, and as a bookmarklet looks up for feeds in the current tab.
Unofficial ones
Fediverse instances
  • Lemmy - At the top of any given community, copy the link from the RSS feed button to the side of the filter and sorting options. Lemmy only hosts local feeds, so getting the link of e.g. an ani.social community through lemmy.world will grant you an ani.social feed, not a lemmy.world bridge.
  • Mastodon - Go to the main page of a given profile and add .rss to the end of the link. Akin to Lemmy, only tracks local profiles.
  • Mbin - Each feed (list of posts) has a(n RSS) feed at the bottom of the sidebar, in the RSS hyperlink right above Powered by Mbin. Allows tracking remote communities, unlike Lemmy and Mastodon, but doesn’t seem to track either microblogging posts or threads marked as +18.
  • Misskey - Same as Mastodon, add .rss to the end of a profile’s base link. Allows tracking remote profiles.
  • Peertube - for one of the feed variants, in a given channel’s main page, click on the arrow to the side of the “Subscribe” button, and in the dropdown menu, get the RSS link from “Subscribe via RSS”; for the other variants, when available, in the same page, look for “Subscribe to RSS feed” (ctrl f if you can’t find), and get the format you want from the RSS icon’s dropdown menu to the right. Unfamiliar how Peertube handles remote profiles.
  • PieFed - In a given community, get the RSS link from the RSS feed hyperlink in the sidebar. Allows tracking remote communities.
  • Bandwagon - With a profile’s link, e.g. https://bandwagon.fm/@some_user, add /feed?format=atom, /feed?format=rss or /feed?format=json at the end of the link, whichever you prefer. Alternatively, go to the page’s source (on Gecko browsers, e.g. Firefox, Ctrl U or by adding view-source: to the beginning of links), look for the links with /feed?format=, and get the link or links you want/need.
Fediverse bots
  • Fediverse bot, RSS Parrot - Instructions on the site. Tested making a feed on both Mbin and Mastodon, but only worked in the latter. After that, users can have a fediverse-provided RSS feed through Misskey, as explained in the section above.
  • Fediverse bot to Bluesky, and vice-versa, @bsky.brid.gy@bsky.brid.gy / Bluesky counterpart - Instructions on the bot’s bio. Testes on both Mbin and Mastodon, but doesn’t appear to work on the former. Then follow the Bluesky mirror for the account through Bluesky’s RSS (instructions in the section below), and the fediverse mirror for the account through Misskey (instructions in the Fediverse section above)
  • Fediverse instance for RSS bots, Ibbit, successor of Pondercat (RIP) - Meta community (@meta@ibbit.at) used (also) for requesting new feeds to be tracked, according to its sidebar. Once included, users can have fediverse-provided RSS feeds through Lemmy, Mbin, Piefed and Misskey, as explained in the Fediverse section above.
Other forums/blogs/microblogs
  • Bluesky - Add /rss to the end of a given profile’s base link.
  • Medium - Add /feed right after the domain, e.g. https://medium.com/feed/@someexample
  • Steam group announcements - get the link from the button at the sidebar of the announcements tab, or more guaranteed since a variant interface doesn’t show it, using the group’s base link (e.g. https://steamcommunity.com/groups/somegroup), add /rss at the end.
  • Tumblr - for profiles with the link pattern https://some_user.tumblr.com/ and custom links (e.g. https://satw.us/), add /rss at the end of the link, e.g.https://some_user.tumblr.com/rss and https://satw.us/rss
  • VGMdb (forums) - Need to check again, but previously could only find some feeds through the page’s source (on Gecko browsers, e.g. Firefox, Ctrl U or by adding view-source: to the beginning of links).
Other sites that have feeds due to their underlying engines
  • Both Blogger and Livedoor (ライブドアブログ)-powered sites - Look for it in the page’s source, e.g. Gecko’s Ctrl U or view-source: for the feed links right after rss+xml and atom+xml mentions (two different types of feeds, so pick the one/ones you want/need).
  • Discourse-powered forums (e.g. RetroPie’s, and these forums look kinda the same) - forum categories and posts both have a (small) RSS button, the former to the side of the category’s name at the top, and the latter to the side in the statistics right below the post’s name at the top.
  • Wordpress-powered sites - By default include RSS options for new posts and comments in their source codes, so Gecko’s Ctrl U or view-source: again.
Stores, store-adjacent and other catalogue-esque sites
  • VGMdb (game & anime albums database) - “Albums Just Added” & “Upcoming Albums” linked in the sidebar.
  • ArtStation - Use https://someuser.artstation.com/rss, changing someuser for the ID of a given user found in its link.
  • DeviantArt - Use https://backend.deviantart.com/rss.xml?type=deviation&q=by%3Asomeuser+sort%3Atime+meta%3Aall, changing someuser for the ID of a given user found in its link.
Comics and comics blogs
  • A Softer World - Use http://asofterworld.com/rssfeed.php
  • Buttersafe - Use https://www.buttersafe.com/feed/
  • Junior Scientist Power Hour - Use https://www.jspowerhour.com/comics.rss
  • Line WEBTOONS - If a series there has an RSS feed, the RSS button appears to the left of the “Subscribe” button near the top right.
  • Safely Endangered - Use https://safelyendangered.com/blogs/comics.atom
  • Tapas - Go to a given series, e.g. https://tapas.io/series/some_series, and add rss/ before series/, e.g. https://tapas.io/rss/series/some_series. Also found an extension that adds a button with the RSS link to a given series’ page (Firefox Add-Ons link)
  • xkcd - Use whichever you want of https://xkcd.com/rss.xml and https://xkcd.com/atom.xml
  • クラゲバンチ - From my experience, RSS button for a given series included in any of its chapters.
News/magazines sites (most gaming and/or tech-related)
  • GamingOnLinux - Home page and each page from the Sections tab that once opened have a “Latest” segment have their own feeds with their respective RSS buttons.
  • GrabFreeGames - Use https://grabfreegames.com/rss
  • Indie Retro News - Use https://www.indieretronews.com/feeds/posts/default
  • Nintendo Life - Use https://www.nintendolife.com/feeds/latest
  • Nova (some Serbian news media) - Use https://nova.rs/feed
  • Ototoy - Use https://ototoy.jp/rss/
  • Switched to Linux - All feeds linked at https://www.switchedtolinux.com/rss-feeds
  • RPG Site - Use https://www.rpgsite.net/feed
  • Waterfox - Use https://www.waterfox.net/blog/rss.xml
  • GOG’s announcements - Use http://www.gog.com/frontpage/rss
Video platforms
  • Odysee - Go to a given channel, click on the 3 dots in the top right, and click on Copy RSS URL.
  • Youtube - If a given channel’s link follows the https://www.youtube.com/channel/some_very_random_code, put this code at the end of https://www.youtube.com/feeds/videos.xml?channel_id to have the channel’s RSS feed. Alternatively, or if the channel’s link follows the pattern https://www.youtube.com/@some_channel, open the link, wait for it to load, open the page’s source (on Gecko browsers, e.g. Firefox, Ctrl U or by adding view-source: to the beginning of links), look for application/rss+xml (Ctrl F helps) and get the link that comes right after.