Why is this bike SO uncomfortable and what can I do to fix it?

Hi everyone,

I have the opportunity to borrow this foldable e-bike (Victoria "SCALYO 3") for a few months, and I test-drove it on even and uneven terrain over the weekend. The shifting is fast and smooth, the electric motor does what it does, and it folds down very nicely – still, at 23,30 kg I wouldn't call it commuter friendly. I have yet to try lifting it onto a train.

However, it is SO uncomfortable to sit on. My ass HURT after 30 Kilometers, and I'm used to doing 60 km city+countryside commutes with my BGM Vitess. The recommended tire pressure is between 2 and 4,5 bars, so I put it to around 3,5 and ended up stopping in the middle of the tour to let more air out, hoping that would help (it did not). Every bit of uneven ground gets transferred directly onto my ass. I can't even sit up when I see a bump coming, since that engages the coaster brake (my BGM bike doesn't have that).

Is there any way to improve this? I don't know a lot about bikes to be honest. My first thought is to switch the saddles of both bikes and try again. But both saddles are very similarly structured.

Thanks!