Apple had a lot of work to do still with dual sims. There’s quite a number of weird quirks from apps expecting only one phone number. T-Mobile’s scam blocker on

Apple had a lot of work to do still with dual sims. There’s quite a number of weird quirks from apps expecting only one phone number. T-Mobile’s scam blocker only uses the physical sim. Messages get confused if someone in a group switched to your other number. Etc. One other one I think Apple has resolved recently is sometimes mobile data will stop working until you disable one of the lines.