The android captive portal settings are responsible for the annoying question mark beside the wifi icon. If the device can't connect to the captive portals, the question mark will appear. And at the latest Pixel 8a (android-os 14 I believe), it will also route the traffic through the carrier network which is clearly not desirable.
The settings can be changed by adb
(https://gist.github.com/tonyseek/bc5b72197ddb15418c61406061720186):
$ sudo pacman -S android-tools
$ adb shell settings put global captive_portal_https_url <some_server_address>
$ adb shell settings put global captive_portal_http_url <some_server_address>
$ adb shell settings put global captive_portal_fallback_url <some_server_address>
$ adb shell settings put global captive_portal_other_fallback_urls