Linux

I got an old Windows 7 laptop that was going to be thrown out and decided to put Linux on it (see previous thread here). Most people suggested I go with the latest stable version of Debian, so that's what I installed. I've mostly used Windows, but I do have some experience with Ubuntu.

The installation went smoothly, but I've had a few problems getting it set up to my liking:

1. 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 https://dl.flathub.org/repo/flathub.flatpakrepo

I hit enter and nothing happens. No error message or anything. I restarted the computer but flatpak doesn't work, either through the software center or the flatpak website. I found a few forum posts with the same problem, but no solutions.

2. 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?

3. 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?

4. 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?

5. If I need to do a clean install, I'm thinking of switching to Ubuntu, since I'm more familiar with the interface. 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?

Edit: Thanks for all the knowledgeable replies. I did a fresh install of Debian 12 (64 bit) with KDE and it seems to have resolved all my problems. Although it's a little slow and buggy, I've had to reboot it twice. I'll try a lightweight DE if that continues.