Have a look at Thingino. Comes with wireguard built in. No idea about the solar stuff though. Maybe run it off a generic 5V solar solution.

If possible: do that on company time. Let the boss pay for it.

Dorsey took care to hire on for the Bluesky staff a collection of LessWrong rationalists, neoreactionaries, VibeCamp anti-wokeist race scientists and crypto developers. And Bluesky still had to asymptotically approach a tolerable degree of moderation and — eventually, despite the CEO and several devs being followers of the test case offender — ban the Nazis.

https://davidgerard.co.uk/blockchain/2024/05/10/jack-dorsey-bluesky-decentralised-social-networks-and-the-very-common-crowd/

Pocketbook also makes great devices, not that well known outside of EU but their software has more features than Kobo and is (as of yet) not in the book selling market so no conflict of interest (and no analytics, contrary to kobo).