I was also thinking the same, but why is this only happening when trying to log in through an app? Visiting lemmy.ml with any browser still works

Plus I managed to log in using Thunder on a different device, but not on this one

Nope, doesn't work. This is probably related to my device, it's very old

if I try to login, I get this error:

HandshakeException: Handshake error in client (OS Error: CERTIFICATE_VERIFY_FAILED: certificate has expired(handshake.cc:393))

Adding this to OP

Luckily there are lots of alternatives ( ͡~ ͜ʖ ͡°)

Yes, I can using Voyager or any browser really

No, I don't

Love this style. Source?

Android 7 :/