Although I make the preparation as your guide suggests, My gmail accounts can’t be log in on delta chat（ver1.20.5）
Do you get an error?
Yes, it always show like:async_native_tls: unexpected EOF, after my google accunt authorizing delta chat and then it starting log in.
i also notoriously experience issues with gmail + non-google email clients. i suspect they purposefully sabotage this use-cases. my honestest advice is to gradually abandon big G.
eof, possible reasons;
your connection not stable
your connection under attack of mitm and-or spy software
delta.chat bug