Raspbian php7 to php8 and nextcloud upgrade how to

I am running 25.0.3 with ncp 1.52.0 on a rpi (bullseye) and want to upgrade to 25.0.7 in a first step and later to 26.0.x
As there is no php8 available from bullseye repos (there are 3rd party with 8.1 available), what is the sequence of actions I need to take to successfully run an upgrade?

The upgrade process keeps uninstalling php8.1 and rolling back the upgrade or telling me that no php8 is available.

Thank you for guiding me to documentation about this.

it seems you are seeing similar problems to me, i had been going the way already to update to 25.0.6 but also this went bad… i thought it might be my fault because i had updated php to 8.1 already a while back for some other reason, but it seems to be a general problem then…