for most wheels an easy and effective thing you can do is to isolate the areas of the arch above the motor along the seal of the wheel body with something like a butyl braid/cord/tape and isolate the area under the handle with a very strong and sticky tape, something like filament tape (tape reinforced with fiberglass) applied along the seams of the two halves of the wheel body under the handle (also in other places susceptible to water leaking in if possible)

a general next step is to seal the controller, lights, buttons and all other connectors and things that look dangerous inside with a sealant

there may also be some vulnerable components/areas specific to your wheel, for that you may have to search some tutorials on youtube/forumse etc

there are likely local EV shops near you that are doing some sort of waterproofing for a fee, they also can help seal the bearings and the motor and some other useful stuff