MacBook freezes constantly but not in safe mode

This is a MacBook Pro, 13 inches, from 2016, running Mojave 10.14.3 First I noticed that the mouse moved in a jittery fashion, like if it bounced around the point I wanted it to be instead of simply being there. Then the computer became excessively slow. Opening a new tab to google the problem took several minutes, and loading each site with possible answers took also a long time. I tried many things, I checked the memory (I have like 30 GB of free space), I turned it on in all the possible modes, and odly enough in Safe Mode the mouse moves normally... but it is still quite slow. There are no Apple stores where I live, but the guy who saw it noticed that it had too much dust inside, and that the battery was expanding. His diagnostic was that because it had so much dust inside it overheated and that damaged the computer somehow. We took the battery out and I'm gonna buy a new one but running my computer in normal mode is VERY difficult. I could use it in regular mode, my job right now is to edit video and you need audio to do that and there is no audio in Safe Mode. Also, in Safe Mode it works at almost normal speed, the mouse never bounces, so it's not a hardware problem... but there is this general slowness to everything that gets much worse in regular mode, plus there is that mouse bouncing that makes clicking on anything extremely hard. I've checked Activity Monitor a thousand times and there is nothing weird. I have run Malwarebytes and it found nothing bad. Except for the battery the computer is perfect in every test I can make... but it still takes like a minute for System Preferences to open. What could be wrong?, how could I fix it?