I found Bouncer to be a good fit for me. Free, open source, and uses regex.

But it doesn’t come with a block list, so you have to construct your own.

https://apps.apple.com/us/app/bouncer-text-messages-blocker/...

I've gotten hundreds on android and they've all been blocked automatically. I do have this ever-present 'Spam detected' line in my notifications. I can get rid of it, but I kind of like seeing it, just in case.

Every several days I'll scroll through in case something was mistakenly flagged, and it never is.

SMS Spam Block is a good free option if you just want to make a simple keyword list: https://apps.apple.com/us/app/sms-spam-block/id1283355601