epub check fails
guide in metadata.opf is incomplete. Missing required element reference.
However, inserting the link to the anchor was perfect.
Calibre 7.10, Linux Mint 21.3 with Mate desktop (No Wayland. IMO Wayland is hardly fit for Beta, so much doesn't work.)
Calibre from here.
https://calibre-ebook.com/download_linux
I do edit epubs, but not like that. I edit in LO Writer and save an extra docx for Calibre. So I never ever have to edit links or the opf etc.
Mostly I set the size of images and set h tags in headings.
I edit bought or PD epubs or converted from Kindle to fix stupid formatting, so never need to edit opf or links on those either.
So no Calibre issue here, but your opf is giving an error I never saw in 10 years.