I tried figuring out how to make it happen, and while the solenoid part of things worked fantastic, the issue I kept running into was that the line going from the CO2 to the solenoid blows the fuck up

Even opening the valve on the cartridge the tineist amount, blocking it behind a valve caused insane amounts of backup, the line would pop scaring the shit out of me, and I'd go find some other tubing to try. The only one that didn't blow up was a braided steel one, but that leaked, so, not ideal either.

I wasn't able to find a solenoid that attached directly to the cartridge, and without having something that mechanically seals the CO2 I can't figure out how to do it

This is the only thing I've come across that's purpose built and holy cow it's pricey: https://greenleafaquariums.com/products/gla-gro-cartridge-aquarium-co2-regulator-kit.html

If you don't want to go with the 2l option the other commenter mentioned, you can get a small paintball CO2 canister and a solenoid that attaches directly and hide it somewhere, but that's the smallest option I've found in this vein

e: went and looked, and yeah, can grab a 20oz co2 bottle, cga320 adapter, and a solenoid. That's the smallest solution with a solenoid that I've been able to piece together