I am running MacOS 14.7.1 with Safari 18.1 and have the exact same issue. I open an email in my Outlook client application, I click on the "Vote" button, it takes me to a new browser window, then gets stuck in a loop - you can never get to a point where you can respond - you just end up with a bunch of browser windows open based on your threshold of insanity trying and expecting different results.
I'm glad I saw someone posted the exact same issue with Chrome - eliminates Safari. I did find Safari --> Settings --> Privacy and the option to turn off "Prevent cross-site tracking" but it appears to be an "all or nothing" - I don't see an option to white list, or only apply the setting, to office.com. Also not sure why voting launches a web browser window from the Outlook application - why can't voting work from within the Outlook client application.
I was able to vote using my iOS phone - but even that was wonky and took me from the iOS app to a web browser page / the MFA loop twice - displayed an error - then displayed the people asked to vote but no option to vote - at one point it took me instead to a "test vote" I setup to see if I could create a polling request - which works fine - then after I deleted the test it magically took me to the original vote and I was able to vote. All in - 30 minutes of my day to get to this point! I suppose I am just lucky that MS still offers Office to MacOS users - have not seen Apple make much progress on their application suite.... $ go into hardware which I totally get!!!
Something else to note in case MS engineers actually read these pages - after I voted on my phone - I went back to the Outlook client application, opened the original email asking me to vote - clicked on Vote and it worked no problem. It did not matter if I had "Prevent cross-site tracking" turned off or on. This sounds 100% like a MS server side problem.
Thanks to everyone for replying so I am not odd person out on a problem!!