No, a keyring is still required, and that’s a deliberate choice rather than a leftover. Mailspring holds IMAP/SMTP passwords and long-lived OAuth refresh tokens for every account, and the only way to encrypt those on Linux without a Secret Service provider is Chromium’s “basic” store, whose key is a hardcoded constant - it’s obfuscation, not encryption. Mailspring detects that fallback and refuses to save credentials with it, so there’s no “plaintext, I accept the risk” option.
You don’t need a full GNOME session for it to work, though. On Arch with XFCE, install gnome-keyring and libsecret, and if XFCE doesn’t start the daemon for you, launch it yourself with gnome-keyring-daemon --start --components=secrets and run mailspring --password-store="gnome-libsecret" (then add both to your session autostart / the .desktop launcher). Step-by-step notes for minimal setups are here: "Password Management Error" on Linux — Mailspring Documentation