Dear @jonas ,
thanks again. I have posted more details on the Linux Mint forum, but so far did not get any help there.
Please have a look at my more detailed description, with links to screenshots (GDebi and Synaptic):
Linux Mint forum thread
Any help is appreciated.

@jonas ok, thanks!

Hi there,
I am very excited about this program, but was unable to install it on Linux Mint.
After adding the repository:

add-apt-repository ppa:jonaski/strawberry

and updating apt, I try

apt-get install strawberry

and I get:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 strawberry : Depends: libqt5sql5 (>= 5.0.2) but it is not going to be installed
              Depends: libqt5sql5-sqlite but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

My config:

System:    Kernel: 5.4.0-88-generic x86_64 bits: 64 compiler: gcc v: 9.3.0 Desktop: Cinnamon 5.0.5 
           wm: muffin dm: LightDM Distro: Linux Mint 20.2 Uma base: Ubuntu 20.04 focal 

Repos:     No active apt repos in: /etc/apt/sources.list 
           Active apt repos in: /etc/apt/sources.list.d/additional-repositories.list 
           1: deb http: //repository.spotify.com stable non-free
           2: deb [arch=amd64] https: //repo.skype.com/deb stable main
           No active apt repos in: /etc/apt/sources.list.d/google-chrome.list 
           Active apt repos in: /etc/apt/sources.list.d/jonaski-strawberry-focal.list 
           1: deb http: //ppa.launchpad.net/jonaski/strawberry/ubuntu focal main
           Active apt repos in: /etc/apt/sources.list.d/obsproject-obs-studio-focal.list 
           1: deb http: //ppa.launchpad.net/obsproject/obs-studio/ubuntu focal main
           Active apt repos in: /etc/apt/sources.list.d/official-package-repositories.list 
           1: deb http: //mirror.ufscar.br/mint-archive uma main upstream import backport
           2: deb http: //mirror.ufscar.br/ubuntu focal main restricted universe multiverse
           3: deb http: //mirror.ufscar.br/ubuntu focal-updates main restricted universe multiverse
           4: deb http: //mirror.ufscar.br/ubuntu focal-backports main restricted universe multiverse
           5: deb http: //security.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
           6: deb http: //archive.canonical.com/ubuntu/ focal partner
           Active apt repos in: /etc/apt/sources.list.d/zotero.list 
           1: deb https: //github.com/retorquere/zotero-deb/releases/download/apt-get/ ./

I have tried to install libqt5sql5 separately, without success.
Any ideas? Thanks!