Ok, if I’m reading this right basically your clutch is not disengaging.
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It won’t shift into gears when you start it in neutral. Makes sense, the clutch is engaged and you’d basically have to slam it in gear, grinding the gears.
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When you start it in gear the car jumps, even with the pedal down. Makes sense, the clutch is engaged, pedal down disables the clutch/starter lockout, so the lockout allows you to try starting the car. Since the clutch is engaged though the starter is basically turning over the motor, the trans, and your drive wheels. The hop is because the engine tries to start but stalls because the clutch isn’t disengaged.
Now the tricky part, what would cause it? Hydraulic clutches are a sealed system so driving through water shouldn’t have allowed any water in the lines. The clutch itself is a mechanical device, springs, pressure plates and an arm that presses against a bearing to release the springs, so water shouldn’t be a big deal for it either. I’d start by looking at the trans while you have someone else depress the clutch. Make sure you see the slave cylinder moving. If it’s not moving, or not moving far enough, try bleeding it.