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You should upgrade or use an alternative browser. I can't figure out why this works on one and not the other. A newer Mini receives messages from Android users. A 2021 iPad Pro does not. Both run 18.1 and each is connected to 16 Pro Max phones on 18.1 with RCS enabled on the phones.
I don't think Messages is connected to iCloud but I also do not know if that matters.
Any ideas what to try or where to look?