I've been using Debian since 1.3. Haven't really ever needed anything else.
I did "experiment" a bit when the decision to go with systemd was taken, but in the end, most distros went with it and it really isn't that big deal for me.
So it's just Debian. I need a computer that works.
Mastodon has user defined word filters, you can completely mute this crap (of course people love misspelling his name).
I wish lemmy/kbin would get something similar it's really annoying to have this fucker in my feed daily.
I can’t figure out how to setup flatpak. Everything seems to be working fine until I enter the last line in the terminal:
flatpak remote-add --if-not-exists flathub dl.flathub.org/repo/flathub.flatpakrepo
Hard to help without logs or error messages. Maybe you could run the command with --verbose flag to see if it prints out something that might help?
I somehow set it up so that my username is not the super user, so I have to type a password in the terminal every time I want to use sudo. Is there a way to fix this without a clean install?
This is default behavior and probably shouldn't be changed. It's a good idea to set up your normal user without root privileges and it's a good idea to ask for authentication credentials whenever you need to elevate privileges.
I somehow set up the hard drive partitions so that the OS is on an encrypted partition, so I have to put in a password for the BIOS to boot up. Is there a way to fix this without a clean install?
Again, if you want encrypted disk, then this is actually good behavior, but in case you want to decrypt the disk without reinstall - it's possible, but not entirely simple or newbie friendly procedure, you need to know a bit about disk devices and mounting drives, for reference, see: https://unix.stackexchange.com/questions/60971/how-to-remove-luks-encryption
I’m used to a desktop interface with a toolbar/start menu that I can pin frequently-used programs to, but with Debian it seems like I need to click “Activities” to do anything. Is there a way to set up the interface so it’s more like Windows in that regard?
You can also tweak and change Gnome with addons and extensions to suit your needs - see https://extensions.gnome.org/
Is there any reason why I should stick with Debian? I’ve heard some people trashing Ubuntu but I’m not sure why. Is Debian better for older hardware?
The same linux kernel (in various versions) is running underneath all the distributions, so it's really just a matter of preference. Since you're new, hop around - try Ubuntu, Mint, Pop!, Fedora, Arch and everything else to see what you prefer.