I picked up a 2G Byte Raspberry Pi 4B locally with 2 year warranty and only €55 inc VAT.
I tried the official Raspberry Pi OS, but found too like Win10. Also though it boots fast, it's sluggish, maybe uses Wayland and lacks customisation. Minutes to install.
There is no Linux Mint with Mate, but there is an Ubuntu 64 bit ARM with MATE, so I installed that, took much longer, like 10 minutes and slower to boot. However I was able to uninstall much Ubuntu OTT stuff and install many of the aspects of Mint (hardly a surprise as both are Debian based). It runs desktop and apps faster than official pi OS, and I knew mostly the 2G RAM would be OK as often only 1.8G is in use on my x86-64 systems. However the 4G RAM version is worth the extra if it's available.
I have an idea that people used to have to compile their own Calibre and the Distro versions are best avoided.
Anyway:
https://calibre-ebook.com/download_linux
This fetches the x88-64 version on all my other PCs/Laptops, but fetches the ARM version on my customised Ubuntu Mate ARM64. from here
https://ubuntu-mate.org/raspberry-pi/download/
I simply right click on any *.im.xz file and my existing Linux Mint writes it to an SD card and resizes to use the free space. There is a utility for Windows users.
Anyhow, the Calibre 7.7 ARM64 version runs perfectly.
Thanks Kovid.