specifically the physics of the player character, where when you jump into water you kind of sink a bit and then just float, and when you go out of the water you have momentum? i just need resources i dont want any scripts or anything.
Water physics insubnautica is just simulated real life physics namely buoyancy.
This could work you could also use the formula F = - pgV to vector force to calculate the buoyancy force.
The tricky part is calculating submerged volume but you can find some tricks even on other engines such as unity as the math is the same.