I've been there. I used Debian too. I'm retired, but if I had to do it again, my choice will be Devuan.
Just for the record: I had no glitches at all in my classroom, and ParallelSSH was a good friend of mine.

I find suitable in my use case hot swappable SATA drive bays. Sure that USB 3.0 is fast enough to backups, but I prefere a real SATA conexion.

I have an USB to ethernet adapter at hand, just in case.

It is well known that since systemd appeared sharing swap partitions between distros in the same box is trickier that it used to be. But I don't know how can be related the swap issue with your DE problem. I see two options: 1) everything works, let's move on; 2) let's dig deeper triying to find the root of the problem. It is now up to you

It can be because of the media player is bypassing the general ALSA settings. I'm not an expert on this, but I know that with VLC you can choose any output for sound, on the fly. Worth trying it.

No Telefónica staff at home

I don't mind what highlighting to use, as long as there is some one! Currently I use geany and nice editor defaults syntax highlighting configurations. My only concern is using white background, I dislike dark modes. Other than that, I can use any colour scheme.

No problem

This is the SANE backed, it is installed in my system, but the configuration of "Scan to USB" is a different kind of thing.

We are very few users. But if we knew the protocol, we could write our own utility. It seems a very simple task.

I bought a document scanner when the lockdown here is Spain. I couldn't find what I exactly wanted, but at the end this worked for me:
Brother ADS-1200

Main advantage: I use the scanner without conexion to the computer, through a USB stick.
Main problem: I cannot run any Linux program to access the configuration of the to USB scanning. I have to use other OS (proprietary).

I have used this device succesfully and extensively. YMMV.

I think that more expensive Brother models with operation panel can be fully used without proprietary OS, but I'm not sure.

Sometimes we do something slightly different and we are not aware of doing it. I'm quite sure that there are good technical explanaitions on what you are talking about.

For more that 25 years I've been learning a lot from what was apparently a malfunction of my UNIX-like system: from Coherent all the way to Devuan. Almost always I was wrong, not the system.

In this very forum I read every day a lot of expert advice.

The explanaition of HoaS about the delay of your system at boot is excelent. I spent a rewarding amount of time reading it. Thanks, HoaS.

My main desktop has a 2TB spinning disk that holds /home; I backup it on a weekly basis, rotating four external disks plugged through SATA. All partitions are ext*. No trouble in more that 20 years; exceptions: disks eventually fail, you HAD to backup all your data beforehand.

I've two servers at home: same policy as desktop, also no problems. 20 years and counting.

Defrag? Nope.

I have a bunch of USB devices with instalers of a few versions of Devuan, both 32 bits and 64 bits, and live rescue systems, just in case.
A solution like Ventoy could save me a few sticks. Using it is in my "to do" list.