Double checked and I am running the latest qBittorrent (4.5.4) downloaded from Fosshub (which is where they link to for downloading).
I also reinstalled python as @burnedoutfordfiesta suggested, making sure Python had access to Path. And I just tried adding 1337x and Solidtorrents through their links copied from that page I linked to, they both come back as "not supported". Every plugin is coming back as not supported, all of them.
I updated the OP with a screenshot of what's happening, taken before I tried adding your suggested torrents through their links, but the message was the same for both.
no such problem for me, are you sure you are pasting correct URL and use newest qbit from official site https://www.qbittorrent.org ?
btw you don't really need anything else besides 1337x (2.0), Solidtorrents (2.1, aka bitsearch.to) and YTS (4.3) plugins
tell me exact plugin which doesnt work
save