Thank you, @guiverc and @walttheboss for your kind answers to my request for help.
I plugged the HDD (as @walttheboss witty made me notice, I had not informed that it is a HDD) again on the Ubuntu Desktop 22.04 (here you have it, @guiverc. Thank you again), and ran dmesg. I can't paste the results here because me, in my stupidity, forget to save it. But I can remember that there was a message of section error.
So, I turn back the HDD on the old machine (@guiverc, yes, the same machine that was running Zorin OS - I mentioned it before in a naïve belief that it would be sufficient to make known that the file system was ext4 - again, a naivety). I tried to load Ubuntu Desktop 22.04 from a flashdrive (live section) but yet could not access the files. But, this time, in the loading screen of Ubuntu Desktop 22.04 an error appeared:
Blockquotefsck from util-linux 2.26.2
/dev/sda2 contains a file system with errors, check forced.
/dev/sda2: Inodes that were part of a corrupted orphan linked list found.
/dev/sda2: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY.
(i.e., without -a or -p options)
fsck exited with status code 4
The root filesystem on /dev/sda6 requires a manual fsck
Busybox v1.22.1 (Ubuntu 1:1.22.0-15ubuntu1) built in shell (ash)
Enter 'help' for a list of built-in commands.
(initramfs) _
So, I searched for a diagnostic and found a simple solution here: fsck error on boot: /dev/sda6: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY
I hope it could help anyone with the same/similar problem.
fsck /dev/sda6
fixed the issue and I could access the HDD again. My wife is happy and my marriage is safe again.
Thank you all. Nothing is like the community.