That should fit, the Note 10 (77.3*162.3 mm )plus is insignificantly larger than the iPhone 8 Plus (77.9*158.2) and that fits perfectly. There is still room at the top of the iPhone, so the extra 4mm doesn't matter.

The case is waterproof by default, however it does not have a charging port. I have cut a small slit into the bottom to accommodate a charging cable, however I cant yet speak for its reliability under torrential rain, as I have only used it once in those circumstances.

Yes, the holder for the bicycle and the holder for the mobile phone... I asked myself the same question before ordering.

Hello, I assume you mean the Huawei P20 Pro. I have the Galaxy Note 8, which is about the same width but longer, and it fits easily.

I can only tell you, that my iphone 12 mini fits pretty perfetly in the size M but i cant tell you how big the L is