I have the sim on an external HDD drive, and i would like to test if there is any improvement by putting the SIM on the internal disk of the pc. If i copy and paste my whole FS2020 folder, will it give me a problem when trying running it from a different location?
Dont want to find out the hard way and spend an entire day waiting for it to reinstall 
Did you buy from Microsoft Store or Steam?
Microsoft Store
If you go to Windows settings > Apps > Apps and features you have the option to move you sim. I never tried it but that’s how I would do it. I don’t think copy and paste would work.
I moved MSFS to a new internal drive recently. I copied and pasted all folders to the new one. After that, windows settings, APPS, Microsoft flight sim, (click) move to new drive (select the drive you want to use) It will then check the drive, see its already there etc.
Without that last step it didn’t work (I left the folders in the original place too just in case)
I moved it from a secondary magnetic drive onto my SSD C: drive using the official windows app method. It worked fine. Massive improvement to load times.
What is the official method, you mean the one I told him to use?
Yes the way you suggested is the way I did it.