Just a thought: Did you clean the bed with isopropyl? I had similar issues with bed adhesion on an Ender3 with the glass bed after a few prints, since I forgot to wipe it down.
On paper-levelling: Yes it's kind of archaic, but it works. And an Ender3 is entry-level stuff where you have to integrate a BLTouch by yourself and compile marlin - that's not something you want to do as a beginner.
The comment derived from me, using a prusa with PEI sheet and their official advice is to wipe it down with isopropyl. But that is totally opinionated and only to be seen as one way to clean your buildplate surface. So, totally fine to use soap and warm water :-) Oh, and it's more readily available in most cases. But could be a quick fix if fats are the cause for the adhesion problem.
Your statements on levelling and probes are also totally valid. For most people, starting with less sophisticated (cheaper) printers, this is a painful learning curve. But it pays off to understand the overall complexity of 3D printers and finetuning - and it's fun to experiment.