Hi @matt howell ,
As I know, we could not force a link to an Office 365 group calendar to open the calendar on that group only.
A link formatted as https://outlook.office365.com/calendar/group/xxx.onmicrosoft.com/xxs/view/month doesn't always open the group calendar referenced in the link.
I tested a lot about the "group calendar link" you mentioned, opened the OWA and only chose group calendar Test01 to be displayed, then got the current link: https://outlook.office.com/calendar/view/month. When I opened new pages with the link you mentioned and the link I got before, both have the same effects, could show the Outlook calendar with "Test01" chosen.
However, when we choose other calendars and then reopen these both links, they will show the calendar status last time we modified, instead of only showing Test01. And it is by design, we could not make any changes to it so far.
So, if you always only need to check the group calendar link, this link could helps. And once you have modified the the calendar status, the next time you opened this link, you will have to manually uncheck other calendars to make it only show group calendars.
If you still would like the specific feature you mentioned, you could create a thread in User voice, then other users will could vote on it for you, Microsoft may notice it and add it in the later version.
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