I’ve released a complete 1.0.0 of my Fedi follow & Share widget.
It only supports Mastodon directly for now, but I’m researching other platforms to include. (psst, if you have a favourite / have built a platform and know its remote interaction endpoints, let me know! The better we all work together, the better the whole Fedi gets!)
https://roosenmaallen.com/2022/06/22/full-1-0-0-release-fedi-follow-widget/
Turns out, it also already supports at least Pleroma and Misskey; definitely try it out and let me know if your instance does/doesn't work!