Hi @nemo87
You are not doing anything wrong. The message:
… is really clear, isn’t it?
You have to upgrade php to at least 8.0 for it to work.
If your pi is running on a debian derivative, then you can use
to easily migrate the current version 7.4 to a higher one.
Nextcloud 16 requires at least php8.0 and can be run with php8.2 at most. So I would recommend you to switch 7.4 to 8.2, so you can then update to the current Nextcloud version, without further php upgrade.
Much and good luck,
ernolf