Robocalls are a huge pain but just as annoying is non-stop spam text messages. No idea why Apple doesn't allow for keyword filtering. Spam and robocalls are mostly nonexistent problems on Android.
i've used Bouncer for years on ios with success to filter non-stop political fundraising texts.
It's not perfect/ideal, but you can basically accomplish keyword filtering using a shortcut powered by a message automation. I've done something similar where during the political season I would have all incoming texts (from unknown numbers) run through an LLM to determine if it was a political message. If so, it'd get deleted immediately.