I found the reason for my increased battery drain when using Wi-Fi.
On January 26, 2026, I installed an app called "UB Connect" from the OpenStore. ubconnect
I uninstalled it shortly after. The app wasn't uninstalled cleanly, and a ubconnect.daemon.service remained in the system.
Whenever Wi-Fi was turned on, this daemon would automatically start, but it failed because the app was missing. This prevented Ubuntu Touch from going into power-saving mode after the screen was turned off.
After uninstalling and deleting all leftover files from the ubconnect app, Ubuntu Touch goes back into power-saving mode with Wi-Fi on, and the battery consumption is minimal like with mobile data.