How to achieve consensus in a network? Proof of stake and proof of work aren't suitable, as they allow anyone to create arbitrarily large amount of nodes, and gain disproportionate amount of voting power in the network.

Proof of personhood is a solution? Humanode has an idea of verifying if users are humans with cryptographically secure neural networks (which is stupid, as neural networks shouldn't be allowed to touch anything that is even slightly sensitive).

Probably the best way would be to use government-issued cryptographic keys and verify them using zk-SNARKs, except that governments mostly don't issue any form of cryptographic keys. There are some countries which add biometry to national IDs, which could be interesting to look into? Depends if there's any way to interact with them. However, the main issue still would be that a lot of countries still exists in 20th century and have never heard of such things, which would cut-off users from them from accessing the network.

Fixing Arch Linux

Invalid signature errors can usually be fixed by resetting Arch Linux GnuPG keys.

user$ su
Password: ····
root# rm -rf /etc/pacman.d/gnupg
root# pacman-key --init
root# pacman-key --populate

SSH with YubiKey

Since OpenSSH 8.2 FIDO/U2F hardware keys are supported. This is done by adding new key types, ed25519-sk and ecdsa-sk (sk stands for secure key).

If you're using Arch Linux, you probably need to install libfido2 package, which is required for FIDO/U2F support in OpenSSH.

ssh-keygen -t ed25519-sk -f ~/.ssh/id_ed25519_sk -C "..."

Resident keys stay on the YubiKey and never leave it; not as secure as a proper SSH key, since it just requires user touch to confirm?

See also: OpenSSH - Configuring FIDO2 Resident Keys, Using a Yubikey as smartcard for SSH public key authentication, Guide to using YubiKey for GPG and SSH.