For what it’s worth, I’ve seen a couple of water-damaged screens with the symptoms you describe, and in my experience they’ve been unfixable (there are ways of fixing some screens with touch issues). The good news is that in every instance, a screen replacement did the trick.
The way an FP angel can help you is by meeting up (if possible) so you can try their screen on your phone, to see if that solves the problem. If it does, you can look at what the options are to get a new one - some angels have stocks of spare parts that you can get for cost, or less, or even for free, though screens are the dearest part among the modules, so your odds of finding one for free are rather slim.