Can't Connect a Mail Account

Hi guys, I’m looking for some help setting up the mail client. I can’t even get past the initial setup.

I’m on the “Connect your mail account” page. It doesn’t matter what account I try to add or how I try to add it, the app just hangs after I click Connect and then eventually seems to give up. No error message.

I have tried a gmail, Office365, and protonmail account, via automatic and by manually entering the server settings, no dice.

I have the official nextcloud docker container (latest stable release) installed on Unraid, and I’m accessing through an Nginx reverse proxy on Firefox/Win10.

Anyone know what’s up?