I have v5.12 installed from debian-stable-main on my Pinephone-Mobian-phosh. Debian rarely updates Calibre, but the version from Goyal’s website updates regularly on my Mint workstation.
I donated to Goyal and encouraged him incorporate libhandy, but he wasn’t even remotely interested, even when I told him that the included eBook Reader was already 99% working on Mobian and that it was the best reader on phosh. He rather rudely asserted that his reader was only intended for desktop use… Sheesh!