Thx for that hinting clarifying answer @Tobias.

I just started to search again for the /usr/bin/ directory and it pooped up, it didn't before because I was searching for /usr/bin/php. In general as of now I didn't get how this ubuntu server really works as a ls -l search from the root directory only gives a snap directory as an entry and searching into that is kinda dead end.

Listing /usr/bin/ I got the following directories displayed:
(/php itself is a reference thats why it didn't show up)

php -> /etc/alternatives/php
php.default -> php8.3
php5.6
php7.2
php8.1
php8.3
php8.4
phpdbg -> /etc/alternatives/phpdbg
phpdbg8.4

So I tried to go to /etc/alternatives/php, but again php is a reference so /etc/alternatives/ is the actually directory to go to. Listing that one gives the following list of php directories.

php -> /usr/bin/php.default
php-fpm.sock -> /run/php/php8.1-fpm.sock
php.1.gz -> /usr/share/man/man1/php.default.1.gz
phpdbg -> /usr/bin/phpdbg8.4
phpdbg.1.gz -> /usr/share/man/man1/phpdbg8.4.1.gz

What I wonder now is if it actually was necessary to install php-fpm versions or if I just could have installed php versions and get things going by pointing the local.config.php file to:
/usr/bin/phpx.yz as I guess you stated already.
Also, maybe php-fpm works better in ubuntu debian?

@TupambAdminOrg [2024.03]

Notes about Alternatives systems:

https://gist.github.com/anwas/4873797fd515c69e6f05d9e6d2880e01
# For command line
## It's important to note that there are four important PHP commands you should update if changing the default versions.
## These include php, php-config, phpdbg and phpize. So, to fully migrate to PHP 8.0, execute the following:
sudo update-alternatives --set php /usr/bin/php8.0
sudo update-alternatives --set php-config /usr/bin/php-config8.0
sudo update-alternatives --set phpdbg /usr/bin/phpdbg8.0
sudo update-alternatives --set phpize /usr/bin/phpize8.0

sudo update-alternatives --set phar /usr/bin/phar8.0
sudo update-alternatives --set phar.phar /usr/bin/phar.phar8.0

@M.Scheriau

When I enter in the console I just get a new blank line:
root@VPShosting:~# php

Same happens if I enter than
root@VPShosting:~# which php

The same is true for doing this inside the friendica folder.

Does that just mean that "I don't get a working PHP with simply calling php on the commandline" or should I worry?

Again, this is most likely related to the -fpm install and I'll have to dig into that.

intermezzo:

Summing up right now:
On ubuntu in the case of friendica the php version the instance can or will use can be set by the conf file in:
/etc/apache2/sites-available/friendicaDomain.com.conf
or the specific friendica config file:
/var/www/friendicafolder/config/local.config.php.

In any case it's probably important to not manipulate both options but one or the other.
Could be important to have in mind what happens when the server software itself get's update or the friendica instance is updated.
In other words, one thing is if the reference goes to the general php setting of the server:
'php_path' => '/usr/bin/php'
When the server updates, the installed friendica version will have to be able to work with that newer php version.
(¿what about the recent ubuntu php update mentioned above by the ubuntu server, where exactly takes that APT check place, would an uninstall of "outdated versions" affect the general setting of different sites and php versions?)

If the friendica version get's updated but the server is stuck on an older not supported php version, there would probably occur issues too.

So one one hand there is to consider where the definition of the php path and version will be placed, on the other if the version itself should be hardcoded or left to the updates. If problems show up, in general terms the bug research does have to look the other way around, what php version is activated and where is that setting defined?

One of the take aways from this right now is that phpX.Y-fpm [=> -fpm] has nothing to do with the extra ppa

fpm = FastCGI Process Manager (FPM)

php.net/manual/en/install.fpm.…

syslog.ident string
Prepended to every message. If you have multiple FPM instances running on the same server, you can change the default value which must suit common needs. Default value: php-fpm.

This setting might address (somehow part of) the tweaking settings "editing php.ini" of friendica and at the same time the specific needs we'll have for example for castopod as we want to host a subdomain of that software for video and audio publications in the fediVerse and there for will need quite high values in terms of MB's, especially for videos.
Also, is there a way to define different values for different sites in the same php version configuration file?
(most likely)

listen string
The address on which to accept FastCGI requests. Valid syntaxes are: 'ip.add.re.ss:port', 'port', '/path/to/unix/socket'. This option is mandatory for each pool.

specific IP or ¡domain! setting?
(for example for a video hosting site setting?)

That list goes on and on so we'll have to search first for what we want to do before checking into it in any case.

The digitalocean tutorial used inicially displayed two entries as variation of the standard entry in a sitedomain.registry.conf file robably only the second is/was neccessary fior the correct setup of php, this has to be checked again, for the friendica sites and the castopod site.

Entry that actually (probably) isn't about the php setting:

 <Directory /var/www/site1.your_domain>
        Options Indexes FollowSymLinks MultiViews
        AllowOverride All
        Order allow,deny
        allow from all
     </Directory>

Entry that affects the php entry:

    <FilesMatch \.php$>
        # From the Apache version 2.4.10 and above, use the SetHandler to run PHP as a fastCGI process server
         SetHandler "proxy:unix:/run/php/php7.2-fpm.sock|fcgi://localhost"
    </FilesMatch>

@TupambAdminOrg [2024.03] you need two PHP's - or better say two ways to call it. The one that is called by the webserver directly (this is either php-fpm or the mod_php in case of Apache2 servers) and the other one in the terminal PHP that is called by the background job. Both should have the same version.

The one in the Friendica config is the client version for the background jobs. That will be used for the long running background processes. In the web server config files you define the one used by the foreground processes.