https://boun.cr/ has been active for years and I use it regularly on shady sites.
Sorry for the "lmgtfy" type of answer, but I generally do that search then pick a site at random.
I think I tried with it with Twitter, Instagram and Google (when they asked me for a phone number and I didn't want to give my real one); this was about two years ago. Does anyone have better results?
If you just don't want to give out your number you could get a second one? Nowadays with eSim it should be easy to get a "pay as you go" number and only ever receive sms.
As long as you expect to only use the number once then they should be fine.