It's working! Just was on Chat with Apple Support, and the steps below worked. I suspect I hadn't signed on to my iCloud account on my phone after the last upgrade, so text forwarding wasn't enabled. Once it was enabled, I enabled my computers which hadn't been done! I was able to text friends with Androids using RCS on my computers.
1 Go to the Messages app on your Mac.
2 Choose Messages > Settings, then click iMessage and make sure you’re signed in.
3 On your iPhone, go to Settings > Apps > Messages, then make sure iMessage is turned on.
4 Tap Send & Receive, and make sure the Apple Account listed at the bottom is the same Apple Account you’re signed in to on your Mac.
5 Tap , then tap Text Message Forwarding.
Note: If you don’t see Text Message Forwarding, make sure you’re signed in to the same Apple Account on both your iPhone and your Mac.
6 In the list of devices, turn on your Mac.