There is some good news for Galaxy S21 owners on Verizon's network as an important update is now rolling out for their devices. There were several user reports that confirmed that after the September 2022 update, their devices weren't receiving text messages. This issue was quite widespread and was even reported by Galaxy S21 owners on T-Mobile.
Galaxy S21 owners suffering from this issue had to wait for hours for text messages to arrive. Restarting the phone also did not fix the problem for them. Turning on airplane mode, removing the SIM card, and reinserting, did the trick for some users, but it was a temporary solution.
It was speculated that Samsung would release a bug-fixing update, and thankfully, the October 2022 security update does exactly that. The Galaxy S21 update on Verizon's network is rolling out with firmware version G991USQS5CVI8. The official Verizon changelog reads, “Resolved an intermittent issue where the device didn't receive text messages.” Along with this bug fix, the update also bumps the security patch to October 2022. You can read more details about the update here.
The issue also plagued the Galaxy S22, and fortunately, the October 2022 update resolves the issue. If you haven't received the update yet, then you can check for it manually by navigating to Settings » Software update and clicking Download and install. If the update isn't available, you might have to wait for some time before the update goes live for your device.