I'm a pianist, and pianists are often very particular about how musical keyboards feel. There doesn't appear to be a very large DIY community around it. Getting a digital keyboard to feel good has a lot of elements. It seems that it's very expensive to design and manufacture a music keyboard, let alone to do it modularly as the keyboard community has. I would expect it to require a lot of compromises that I wouldn't be willing to deal with except as a hobby project.
Synths, on the other hand, have a HUGE DIY community and that sometimes extends to making keyboards. But for me, it rarely seems worth it to fabricate a keyboard when a MIDI controller with MIDI cables or MIDI over USB can be had as cheaply as $50 or to have a really well done one for under $150.
I'd be more interested in modding an existing keyboard than I would creating my own from scratch.
I found this list of links related to diy instrument and synth making in case you're interested. https://sdiy.info/wiki/Online_resources
This is such a niche topic that you should probably seek out a traditional forum. Also, check out Look Mum No Computer for some inspiration.