I don’t know about Facebook, because I don’t have an account there, but I do this with Twitter. A new item on my website gets automatically tweeted with using a script that calls a Twitter API. I certainly don’t pay Twitter anything. If they start charging for using the API, I’m out.

From the OP

>"As of 2022-11, Twitter is rejecting new API access for applications used to POSSE/backfeed"

No idea if they will cut off old keys.

You don't have to automate it. "Manual until it hurts."