Doesn't matter how much you paid, MultiMC is an open-source alternative to Mojang's launcher, it still requires you to have purchased the game and it downloads game files from Mojang's servers, so you're getting the same exact game with all the functionality (including Realms if you're into that). If the Mojang launcher is not even letting you start the game without technical issues, then is it really worth it to waste your time on trying to make it work?
If you're still stubborn on using Mojang's launcher... Just making sure, but every time you uninstall the launcher via control panel, you're reinstalling it with the "MinecraftInstaller.msi" file you downloaded from Mojang's website, right?
Try downloading an .exe version of the launcher from here and see if it changes a thing: https://www.minecraft.net/en-us/download/alternative/
Another idea: try making a new Windows user account and try to install and launch Minecraft from it, see if anything changes.