confusion about backing up Messages in iCloud

Hi, I'm really confused about how backing up Messages/SMS works on ios (as of October 2022). I have text threads lasting years that take up a lot of space. I'd like to free up space while also saving all of these texts and being able to view them later. I've explored various third party options and they all have a lot of drawbacks -- a lot of them don't work on my very old macbook (2011-era), the few that do take forever, many are kind of pricey, and none let you save every single conversation from every person you texted all at once (in iMazing, the only software I've gotten to work, you have to save each person's text history individually, and it takes a while).

My understanding is that if you back your texts up in iCloud, you a) can't actually view them and b) if you delete them on any other Apple device, they're deleted from every device.

I'd really love a(n ideally free) way to back up text threads so that i can delete them off my phone and have them saved somewhere permanently where I can easily view them again.

The closest solution I've found to this is backing up texts (ichat files) using the desktop version of Messages, which I'm going to do, but it'd be great to be able to do it on the iPhone.

Thank you!