IOS has had native RCS since they launched IOS 18 back in like August/September-ish, I haven’t had much issue with support from IOS to Android RCS side, I have however had issues with communicating with my mom, but I believe it’s because she doesn’t understand that when she has RCS enabled, and she turns off data, it wants to try using RCS, then fails, and then falls-back to SMS, which for some reason Samsung Messages struggles with.

Personally speaking though, my S20 hasen’t had any issues with RCS period, its always been other devices not actually sending proceeding to error and then the person not noticing it so therefore not retrying