You can still use Beeper[0] and similar. The key issue with this type of application is that some networks have put more resources to detecting them and gotten more hostile to users of it - mostly those who tie ad revenue directly to messaging (although officially it's to avoid spam + detect compromised accounts).

[0] https://www.beeper.com/

I was surprised to see that Beeper actually has support for ‘local bridges’ that connect to services on-device (which reduces the risk of bans and removes Beeper as the middleman).

I was unsurprised to see that (at least with the local Instagram bridge), Beeper is extremely inconsistent with push notifications and sometimes has messages missing in the chat.