Why has my App Store stopped connecting on my iPhone15 SE I have wifi

You need to have a good Service & Wi-Fi.

If they are On, turn Off Hotspot & VPN.

Charge the battery > 70%.

Read again -> Related Article: If you can't connect to the App Store, iTunes Store, or other Apple services

If you have followed all the steps and instructions and if you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK) 

I don't think you're likely to get an answer here… I have a similar question, and they're all answered with absolute garbage non-answers that are not helpful whatsoever by the same user… rainya or something similar to that… Just go ahead and follow her advice… Delete the app and reinstall… Except in this case, the problem is the App Store itself but you can't do it… I have the same problem and there does not seem to be any help