Although I've just enabled it (Chrome/W10), I'm still not seeing anyI'm with you. Although I see the new UI controls (drop-list for moderator notifications, checkbox for hashtags) I don't see any hint of notifications, even when I deliberately take an action that should provoke one.
I checked Firefox's exclusion list for sites where I've blocked notifications, Groups.io was not in that list. I've now added it as Allowed. I turned off Cortana's hiding of notifications because it thought I had a window full screen somewhere.
No clue what else to check.
At least I found out where to look - in the address bar or hanging under it (if browsed to Groups.io). Not sure where if it is a push, probably lower right corner of the main display, as Thunderbird does.
Firefox 77.0.1 (64-bit)
Win 10 Pro 1903.