I dunno why but this immediately made me think of Uplink https://en.wikipedia.org/wiki/Uplink_(video_game)

There is also Cascade Studio (Demo). Sadly development has stalled, it was a really cool project.

Probably not at all what OP is looking for though since TinkerCAD is just sketch/primitive type workflow, not like openscad.

Gatgetbridge (your link) has a breakdown of devices they support https://gadgetbridge.org/gadgets/ . You can click through the vendors to find devices which are both “highly supported” and “no vendor-pair”. Meaning most/all the features work without any reliance on the vendor app.

As for the similarity you are asking about with pixel->GrapheneOS, there are very few watches that can run an alternative open source firmware or operating systems apart from the ones that are already open source, like bangle.js, pinetime, etc. Wearables are even more specialized than phones, they require specialized code designed specifically for them and would likely require pretty extreme effort to reverse-engineer.

I use a pebble 2 HR with gadgetbridge but the watch it self runs the old pebble firmware which gadgetbridge talks to. This is fine for me, but if you are looking for a more modern watch you may have to make some compromises.

Ok, I’m prepared to be downvoted today so here goes.

Nextcloud is an enterprise cloud suite. The one you run in docker on your rpi (or whatever) is the same one that is run at a company, albeit with more high availability and redundancy, but the same application, proxies, caching, db, etc. Nothing is stopping you from running the stable channel and testing your upgrades, or even rolling out specific stable client versions to your devices.

Said companies often have teams (more than one person) to run it, stage upgrades, automated testing, automated backups, monitoring, etc. They go to work and do just that, maybe not every day but at least a couple times a week their focus is Nextcloud and only Nextcloud.

What many people in the self hosting community do is spin up docker, without ever having touched docker before, and try to run Nextcloud, forget that it exists, and then upgrade it a year later across multiple versions without maintaining the database. Then they obsess about how fast an app loads by refreshing it a whole bunch, and then complain on internet forums that it sucks. This, like many posts, doesn’t have a specific problem for us to help with, no logs or stack traces have been posted, and the subject of the complaint shows just how terrible your understanding of application security is.

So, while there is legitimate criticism of some of Nextcloud’s design choices, this isn’t it. And at the risk of sounding a little gatekeepy, if you post “nextcloud updates break everything” with no context you probably should spend some time gaining a better understanding of how internet facing services work and make an attempt to fix the problem (probably misconfiguration, and in this desktop client case probably a heap of un-updated local software installed alongside the client), which I’m sure people would find if they did the bare minimum of reading a few log files or any of the other things that come with being an application admin.