Why are you going through all this effort to have a multi-OS setup when reselling the machine anyway? Let it be the next owners issue, IMO.

Yes

Interesting. I happen to have bought into the hype back then and so I still have a 4G 700 model. I may resurrect it. No idea for what, but 32 bit has it's perks

Here's yer wing nuts folks!

There's ones left and ones right, so plenty for everyone, so stop arguing!

Yes

Post the content of the file /etc/apt/sources.list (use the code button to mark it from your normal text)

You may need to enable particular repositories.

I'm not sure that's actually a benefit for users. Cause pretty much any potential buyer will abuse the massive userbase to sell even more personal data for even more money.

But since when was user-privacy of any concern to corporate US Gov't

From what I understand, it's a kernel thing. I'm not familiar with the particulars, but rebooting is never a bad option in such cases.

Clearly, you've missed the memo: Linux is not Win-OS!

In Devuan, like all Debian-based distro's, you add a repository to the /etc/apt/sources file. Then add the key to that repo via apt/dpkg, refresh apt via

apt-get update

then install any package from that repo via the normal method

apt-get install <package-name>

Removing it is as simple as

apt-get purge <package-name>

The purge option tells apt to completely remove any traces of the package, including config files and whatever else it installed/used, from your system.

If you want a GUI to help you out, Synaptic takes your hand, just explore the menu for the correct function.

You do NOT manipulate a database manually, like some Win-OS users seem to have taught themselves

I tried to stay out of this, I really did

Genetically modified foods (hyperfoods) are widely available in the US, where food standards are deliberately low to allow big farm maximize their profits.

Look where it led them 

Yes, hyperfoods are bad for your health. Which is why the EU has banned them. As a result, the population over here clearly has better judgemental powers to keep extremists out of a position dominating the various political stages

Brother offers a complete install script for MFC devices, which works based on some simple questions like model number etc. It installs and configures everything you need to get your Brother MFC working. It's also on the Linux support pages, in the install section. It worked a few weeks ago for my Devuan Stable install for a older (ancient?) MFC device. Make sure you run the installer as root! (it fetches and installs dependencies via apt/dpkg (can't remember))

I take it you've visited the LTSP pages?

https://ltsp.org/

About 15 yrs ago I managed to set up an LTSP server and to boot a client from it. Don't fool yourself, it's quite a job to set up the entire infrastructure: DHCP, FTP, DNS and only then LTSP as such. Effectively, you're setting up a very localized but complete mini-ISP. It can be done, I did, but it's worth getting pretty comfy on the CLI, cause you'll use it a lot. It also requires, due to DNS and DHCP, a physically separate network. Technically you might be able to get stuff working on your existing network, but only if you have unrestricted access to the router of your home network. Basically, you need to know what you're doing and if you do, you didn't have to ask

There might be something else going on you probably don't realize. Do the following:

su #become root, alternatively sudo su
fsck /media/<user>/<UUID> #check the file system for errors and repair if required
chown <user> /media/<user>/<UUID> #make sure the directory is owned by the user
chmod 777 /media/<user>/<UUID> #set permissions for the directory for general access

HTH!