Shared Calendar Issues

Hi all,

I'm trying to create a shared calendar for a few coworkers and I'm having issues with successfully allowing anyone to open it. Unfortunately, half of the staff uses various versions of Outlook and I think it may be causing issues

Two of my coworkers had this error (I'm assuming both were on some ultra old version of Outlook): https://i.imgur.com/MfvJs6k.png

Two other users got the invite but no accept option was visible (both using newest version of outlook, I edited out the private information but the rest of the invite is exactly how it appeared): https://i.imgur.com/kYCdkCM.png

And after various tests sending invites to myself and going through OWA, desktop app, etc, I was able to successfully import the calendar by unchecking this option in the outlook desktop app(in which case it accepted, sent me to the OWA page, made me log in twice, and then proceeded to add the calendar): https://i.imgur.com/rOt2egC.png

I saw a lot of various solutions online when searching google and unfortunately, remoting into my coworkers PCs and applying Outlook updates isn't really an option. I was more so coming here to ask if the issue is related to the different versions, and if so, do you guys have a better method of creating a shared calendar that isn't just an excel spreadsheet, or a relatively simple fix to my current issues?

Thank you!