Hello and welcome to the forum @Sprookun!
I would like to start with your second problem, the fact that Krita does not run smoothly. This is most likely due to the extremely low performance reserves of your PC, 4 GB of RAM is an absolute minimum for Krita, and a mobile E3 processor with only 1.7 GHz clock is sufficient for web browsing or office, but for larger images, images with many layers or even longer animations you will quickly reach the limits of your laptop.
Now to the disappeared submenus. In most cases it has helped to delete the preferences files. The downside is that you have to set up Krita again, so you have to customize it again to your needs. Unless you have customized Krita a lot this is not a loss, I just wanted it said before, but think since you already tried a (useless) reinstall you don’t care about the settings.
I’m assuming you’re using Windows. On Windows, Krita’s preferences files can be found in the path “c:\Users\YOUR WINDOWS USERNAME\AppData\Local\”, they are usually “kritarc, kritadisplayrc, krita-scripterrc, kritashortcutsrc, klanguageoverridesrc”, although not all of these files need to exist, they are at the end of that path and not in a subfolder.
If you can’t find the path “\AppData\Local\” you have to enable the hidden files and folders display first, how to do this you can read here If you work on a Mac or Linux system you can read here where to find these settings files.
Michelist