Conclusion:
Calibre 5.11 is OK on Linux Mint 20.1 without doing
Code:
sudo apt-get install libxcb-xinerama0
That fixes 18.3, but 18.3 support ends in April 2021.
The 19.0 is not a good version of Mint.
The 20.0 is not a good version of Mint.
Mint 19.3 is good and fast and supported for a reasonable time, it's 32 bit and 64 bit versions. It may or may not need libxcb-xinerama0 installed.
Mint 20.1 is good and 64 bit only.
So Calibre 5.11 with Apprentice DeDRM 7.1.0 is fine on Linux Mint 18.3, 19.3 and 20.1 with the Mate Desktop. I don't recommend 19.0 or 20.0. Only Kindle books for PW3 via PC download tested.