Make SuperProductivity modify a local .ics file

[Luca-Jank]

I want to start organizing my workflows with SuperProductivity.
I also use Mozilla Thunderbird, and would like to have a synchronized calendar between SuperProductivity and Thunderbird. The calendar file used by both programs is stored locally on my PC.

I registered the .ics file in SuperProductivity.
Adding an Event in Thunderbird modifies the .ics file and it'll show up in SuperProductivity, which is great.
However, it doesn't work the other way around - SuperProductivity seems to not modify the .ics file no matter what I do, and therefore, nothing registers in Thunderbird.

Is there an easy way to make it so Events registered in SuperProductivity are actually stored in the .ics file?

I've read a bunch about WebDav, and I suspect this might work for me, but it looks a bit daunting. I would prefer a simpler solution for my specific use-case if one exists.