Problem with Dex and Screen Timeout

I have for two years used Samsung Phones (S20 an S21) and Dex cable for running Zwift. It has worked super! But now, problably after software upgrade in phone, the screen goes black when screen times out. I have longest possible screen timeout which is 5 minutes. For security reasons (work phone) I am now allowed to switch screen time out off.
What can I do? Anyone else having the same problem? As you understand it is extremely annoying to have black screen every fifth minute when zwifting…

I have a different issue since recent andriod up date

Samsung s 20. Tv, cables the same as used for years.

I plug the phone into the TV. Phone states connected but nothing is displayed on tv. Checked all the AV channels. I get the dex track pad on the phone.

I’ve tried on a newer TV and all seems fine.