This way, pianoteq is always readily available to my user account(s) simply by typing or launching "pianoteq" and also as a VST, and i don't mess up my filesystem by having random files all over the place We could debate all day which is best between installilng pianoteq as normal user or root, but never run it (or your DAW/host) as root.

Ah, good question. I am installing Pianoteq Standalone.  I extracted the pianoteq zipfolder in /usr , because I thought that makes sense, but maybe that is stupid for some or another reason.

Not exactly "stupid" but unnecessary, unless there are multiple users logging into your computer and all of them want to use Pianoteq. If that's not the case, do this:

1) Completely delete everything related to Pianoteq you have installed. Remove the Pianoteq folder from /usr, remove the whole directory /home/myname/.config/Modartt - you probably have to do all of this as root. This is important because leaving something root-owned somewhere in your directory structure may prevent you from later using Pianoteq correctly.

2) As a standard user (not root), unzip the Pianoteq directory into either into /home/yourname/Pianoteq or /home/yourname/bin/pianoteq/, or even /home/yourname/.vst/ or anywhere where you are used to install your instruments. You can also unzip just the single executable file, not the whole Pianoteq directory (I am not quite sure what's all included in the directory).

3) That's all. Afterwards, just navigate to relevant directory and start Pianoteq executable.

Afterwards, you can create a Pianoteq launcher icon or create a link to be able to launch "pianoteq" command from the commandline, regardless of the current directory. If you want to do either and don't know how, I can help you (although I use Xubuntu, not Mint).

Please describe what you are trying to achieve. Running Pianoteq as standalone? As VST plugin? For which DAW software?

I have some problems with the installation of pianoteq on linux (mint). I am relatively new to linux, so it must be partly my lack of understanding of linux, but anyhow:

I managed to install pianoteq, but I did not manage to activate my key, it tells me (after inserting my serial code):
"Could not save the activation key!
Please check file permissions of /home/myname/.config/Modartt/Pianoteq56 Stage.prefs

I checked and found it was root-owned. So, I changed it so that I am the owner with read and write rights, but that didn help.

Any idea what I am doing stupid here?

Thanks a lot in advance!