Automate 2-speed bathroom fan with Shelly

In my bathroom I have a 2-speed fan from Helios model ELS-V 60/35.

It has 2-speeds: Speed 1 (lower speed) is constantly running no matter what. That what it does already and should keep doing. It is never supposed to completely shut off. Then I have a manual switch which I can press to put it into speed 2 (higher) e.g. when I take a shower. It is not coupled with any lighting or anything just controlled separately with that wall switch. When I switch off at the wall switch it goes back to speed 1. According to the electrician there is no neutral wire at this switch

I would like to do is put a Shelly behind that wall switch so that I can automate when the fan is going to speed 2 (e.g. in combination with a humidity sensor).

I think I need to use a Shelly 1L as it does not require the neutral wire, right? If so can I just put the Shelly between the switch and connect the existing wires and that is it? I also saw there are bundles with a “Bypass”. Do I need that as well or what is it for?

Thanks very much