Do you use the correct version with your webserver?
I think you use the snap version from php (snap and apache2/nginx).
I hate snap and do not understand the software. Sorry.
Which snap version do you use? https://github.com/nextcloud/nextcloud-snap
In the package you can read with php version is used.
It is snap. You can not really change things. Sorry.
Yes, the memory-limit is the only php setting that could be set via snap set .
source: php-utilities
The upload_max_filesize is set hard in the config files. (I linked it in the post before)
; Configure larger uploads than the default
php_admin_value[upload_tmp_dir] = ${SNAP_COMMON}/nextcloud/tmp
php_value[upload_max_filesize] = 16G
php_value[post_max_size] = 16G
; Allow for a dynamic PHP memory limit
php_admin_value[memory_limit] = ${PHP_MEMORY_LIMIT}
The snap package is a out-of-the-box solution, managed by the snap-devs, so users can run a safe nc-installation without special knowledge. Most settings are not meant to be changed by the user.
I would also prefer a self-managed installation with the help of my own scripts. If you want to have a deep understanding of your setup or you want a different setup you should not use snap.