Also, if you use Firefox; it depends on pulseaudio.

Exactly. But with the help of apulse you can use stardard Firefox downloaded from mozilla.org with ALSA and not use pulseaudio.

What I normally do to disable pulse:
edit /etc/pulse/client.conf:
set autospawn = no
remove any <home>/.config/pulse that exists
Not sure about KDE, but there is probably an entry for pulse to auto startup (somewhere in session?); disable this.
reboot.

Hopefully now running without pulse.
Play some sound.
Enter alsamixer in a terminal and use this as your mixer.  You may have to press F6 and set your sound card to the "actual" sound card instead of "default".  Other things to do in alsamixer are to set the volume levels.  Make sure no "MM" at the bottom, thats mute; hit M to unmute.

To remove pulse; you can open a terminal and enter apt-get -s purge pulseaudio and see what it screams about.  If it wants to remove important packages, then you may not be able to remove it; not sure about KDE.  My personal experience with XFCE and LXQT is that the dependency on pulseaudio is at the meta-package, as well as "some" of the real software packages installed by the meta; thus pulseaudio can be removed, as long as you arent using a particular package that depends on it.  I do not have pulse installed and can happily use mpv, for example.

Also, if you use Firefox; it depends on pulseaudio.

On x86 desktop, to record and to play, you need to pass by the mega sound system pulseaudio. Pulseaudio locks all what comes as "stranger" which is not pulseaudio.

It is a drawback for full use with device access freedom, but ok for regular user desktop (e.g. mouse click only).

Ist is maybe possible to remove pulseaudio from kde, likely with another sound system?

thank you very much in advance.