This is purely anecdotal, but I used to post and engage with Facebook a lot more earlier in the year, both with my own posts and liking others, commenting, etc. Whenever I posted an event or something that I wanted to share, it seemed to get a fair number of likes and shares.
Fast-forward to later on in the year, and my engagement with Facebook has dropped off a cliff by choice - I haven't posted anything in the last six months and hardly like anything anymore. I barely go on the site, but I still deem it valuable for sharing information since a lot of my friends and acquaintances are on there. I posted an event that I was organizing and it received very view likes and no shares. I re-posted a few weeks later and the same thing happened - maybe a handful of likes whereas I would normally get at least 10x that.
Does Facebook promote posts from users who themselves post more frequently over posts from infrequent posters? Maybe my last couple posts were not as interesting as before, but it just seems like there was such a difference in engagement that there might be something in the algorithm that's demoting (or not promoting) my posts in the same way as before.