A password manager that can keep passwords on one device, and use the passwords on the other, without the storing one being connected to any network, etc
KeePass with inputstick. It's a device that plugs into a USB A port, and your phone talks to it via Bluetooth. It emulates a keyboard (and mouse if you want), and there's a KeePass plugin for KeePass2Android.
You open one of your password entries, click the username, and it types the username on your computer via inputstick. Ditto for passwords and totp or other fields.
You can also use inputstick to just remotely control your computer, albeit locally only and without a monitor connection. I've used it to control my raspberry pi or android TV, aside from password entry.
With this, you can have your password database be completely offline and your computer have no lasting knowledge of your passwords. Of course, a keylogger would still get the passwords that are "typed".
I've had one of these $40 devices for a few years. I don't use it too often, as I tend to synchronize my KeePass database on all of them, but it does come in handy. I wish the developer of the hardware made a usb-c one, but it works with usb-c to usb-a dongles.
Hmm, it seems I missed this, saw the plugin many-many times, but thought it works with USB cables
Interesting, sadly I can't get my hands on any inputstick (the area I live in is very harsh on importing stuff except local marketplaces(which don't have the device))
At the same time it uses Bluetooth, which makes it not fully airgapped
Maybe some time later I will get into developing something similar, but wity nrf chips