Brakes fresh Debian. Where to look for an error?

Question

Debian

I'm trying to get to know Linux better. Many times I tried to install the system next to the 10th Windows . I made a lot of mistakes and decided to install using the guide ( https://info-comp.ru/install-debian-10-next-to-windows ). I did everything according to the instructions, except for the item about packages (Step 16 from the guide above). The author missed the moment with the mirror, but on the contrary, I decided to use swapping from the archive. Maybe it has some meaning.
In short, as soon as the system boots, everything starts to hang heavily. That is, at the moment of entering the user. You hover over the application icons and see 2 frames per second, figuratively speaking. It's impossible to work. I tried to open the browser, so it's even worse there.

It also seems like I opened a program like a task manager through the console with the "top" command. Not a particularly user-friendly interface, but it seems that at the moment, for example, hovering over application icons, the processor is heavily loaded.
Lord experts, where to look for the root of the problem? Tell me please.

Edited: No need for me to suggest other distributions. I would like to understand what is my problem