Can the $10 keys be used for GPG and SSH key unlocking or just something web authn specific?
It's the "Yubico Security Key" (https://www.yubico.com/pt/product/security-key-nfc-by-yubico...) which supports: WebAuthn, FIDO2 CTAP1, FIDO2 CTAP2, Universal 2nd Factor (U2F). So, should work.
No, the e-mail i got from them say it is the Yubico 5 NFC or the Yubico 5C NFC
that does have PIV and PGP modules.
https://www.yubico.com/br/product/yubikey-5-nfc/ https://www.yubico.com/br/product/yubikey-5c-nfc/
You can use PIV for SSH just fine.
It's not OpenSSH's weird FIDO mode, but I don't like the FIDO mode anyway because it requires storing a file on the computer.