Why are my Messages on my iPhone ios 18.3.2 and my macOS 15.3.2 not synching?

I have the same issue and just posted it. I contacted Apple Support last week but not response. I've gone into Messages in my iCloud account to request a sync, but any text to an Android phone is not synching.

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 and it is now working! 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.