Development on Spectacle ceased[1] and it looks like the community may have rallied around an open-source program called Rectangle, which is open source. At least, judging from this single Reddit thread lol:
https://www.reddit.com/r/osx/comments/kazpcn/spectacle_alter...
[1] Although when I search for it now, I see an update from 2023 on softonic? Although the original dev's github repo for it hasn't been updated in years. https://github.com/eczarny/spectacle