Battery self discharge is measured in days at worst, more typically weeks or months. It should not be dropping 5% over the course of an hour or so even if the device is a bit warm. Plus having it plugged in should start charging again once the battery starts dropping too low.

You shouldn’t see the battery drop if it is not using the battery, which is what pass through would suggest.

They changed it recently where you can have two members of a family able to play two different games at ones (or rather number of copies of the game at once).

But that requires different accounts even if one account owns all the games.

Sounds like a stuck button. Personally I would disassembly the device and have a look at the button and surrounding parts for any damage or liquid or debris at all. If there is any physical damage then an RMA or maybe replacement parts can be ordered (like you can buy replacement rubber if that feels worn at all). Otherwise I would ensure everything is clean and free of and liquids, stickiness or debris then reassemble the device. Even if nothing looked wrong I would test it again and see if the act of disassembly did something to solve the issue which it sometimes does for things.

IFixit has guides for the LCD and OLED versions and overall the steam deck is not very hard to disassemble compared to other small electronics. Though if you are unsure about this you may just want to talk to valve support first. If you accidentally damage something that could affect your ability to get an RMA.

I saw that when playing a game, it counted the time since it was opened while playing. But always saw it correct itself to actual time running withing a few seconds/minutes of closing the game on the deck.

That is a lot of contradictory sets of requirements. If it is important to have on the deck then it is going to be trivially searchable online. Something that is niche that others are not really doing is going to be very subjectively interesting or useful. That makes it impossible to recommend anything without violating one of those requirements.

Instead here is some advice for finding project ideas: Look at your own interests/hobbies/things you need to do and start taking note of problems you encounter, grievances or annoyances you have or just things you think could be made/done easier. Out of those you can look at ones that you think a steam deck could help solve and from that you can start to investigate ways to use the steam deck to solve those problems. That is essentially how you find niche and interesting/useful things that are specific to you to work on. It can take time, but the more you think about it and write things down the easier it becomes to find projects to do.

Things that I can just easily stop.

Technically any non-online game will work since you can just put the steam deck to sleep with the tap of the power button when ever you want and resume later on. It takes a couple of seconds to go to sleep and so the only times it is annoying is when you are directly in the middle of some action - which is generally easy to avoid in most games if you know you are coming up to your stop.

Personally I have been playing monster hunter world like this which works quite well - especially since there is quite a bit of less action packed stuff you can do between the main story line.

Not quite the same as you have no tactile feed back on when you are about to enter the full pull part.

And given some recent news about Valve working on an ARM emulator and funding Arch Linux to help them start supporting ARM as well they might be working towards that. Though if that is for the deck 2 or something else further in the future is yet to be seen.

The only other major thing for repairability/upgradability would be less glue on the battery and threaded inserts, which doesn’t add size.

The glue was reduced on later versions and especially on the OLED version which also got threaded inserts. So those are already done and I doubt the next version would regress in that regard.

I don’t see why this would help. More likely there are two different teams/people working on either side separately from each other. I bet the windows work involves a lot more work on Microsoft’s or the chip manufacturer’s side than valves.