Hello Adeybaby,
Welcome to Apple Support Communities!
We want to help ensure Airplane Mode is working as expected on your Apple Watch and iPhone.
Let's start by checking your settings to mirror Airplane Mode with this step:
"You can set your iPhone and Apple Watch to mirror the Airplane Mode setting of the other device. Go to the Watch app on your iPhone, then tap General > Airplane Mode > Mirror iPhone."
This Apple Support page has the full details: Use Airplane Mode on your iPhone, iPad, iPod touch, and Apple Watch - Apple Support
If the issue continues, toggle the setting and then test again.
We hope this helps to quickly isolate and resolve the issue to get Airplane Mode mirroring on your devices again.
Cheers!