A cloud-based service included in Microsoft 365, delivering scalable messaging and collaboration features with simplified management and automatic updates.
Based on my test, this is no option to edit the MailTips for DL as the same way to mailbox. And only way is to use powershell:
Set- DistributionGroup groupname -MailTip "<MailTip text>"
“Also looks like connecting to MSexchangeOnline now disabled as an option.” Did you have any issue to connect to EXO powershell?