I'm sceptical of evaporative coolers. In the short term it might work well, but it increases humidity. That leads to sweating being less efficient and generally a worse situation than before.
There would need to be a way to remove moisture from the air, which ironically was the original purpose of air conditioners, not temperature.
Last commit is two years ago. I'd recommend checking what you have installed. A quick search on GPlay finds what appears to be a clone that may or may not leak user data.
OpenBoard is no longer maintained. Heliboard is a good alternative.
I think Google Play on Graphene is a good compromise, since at least it does not have root access. Unfortunately it is very crippling to completely avoid Google on Android.
That being said, I heard others are using work profiles to isolate all apps using Google Play from their more private apps. I'm not doing that, but work profiles are nice for ... well work apps.
The option to use TOTP is already well hidden. It's not like someone who does not know what he is looking for and uses an Authenticator already will accidentally select it.
I mean, other file sync apps upload everything to a third party while you're working with the device.
Then, when you use another device the first one can be turned off.
Solaar usually works well enough. Not sure if the gestures part is supported on MacOS.
I usually avoid depending on "hardware support" software for reasons like this. Once the software is no longer supported or as seen here, introduces some dumb "feature", it becomes annoying.
Even central currencies can work if you can make offline and peer to peer payments.
Not easy to pull off cryptographically, though.