As long as you only want to message just a few contacts, Threema has an unlimited plan for a limited number of recipients (15ppl/~5€pm - https://threema.ch/en/broadcast/pricing). Only the gateway service you listed is quite expensive.
I heard iCloud Login on 2FA incompatible devices is possible by entering the otp code directly after the password into the password field. Seems to be some undocumented backwards compatibility feature.
watchOS 7.0.2 contains improvements and bug fixes, including:
• Addresses an issue that could cause the battery to drain more quickly
• Resolves an issue that prevented some users from accessing the ECG app in regions where it is available