HASS OS - possible to install other services on RASPI?

Hi, I‘m quite new with HASS… installed the OS on an Raspi3, works…fine!
Now my question: is it possible to install other services beside HASS on the PI…for example pi-hole or AdGuard?
If yes, how do I access the PI via ssh without disturbing HASS?
Regards, Michael

Check out add ons… Probably what you are looking for.

Settings > Add-ons > Add on store (button bottom rt.)

Yes, AddOns … I started using them (File & VS Code Editor) and saw others… but I want to use additional programs / services on Raspi which are not realised as add on.
Using HASS OS means no other installations on Raspi?
It looks like instead of using HASS OS the usage of the ‚normal‘ Bullseye installation with HASS in docker would open me the possibility to use the Raspi for additional things … is that correct?
Regards Michael