Late 2015 iMAC OS upgrade with microsoft 365

I have a late 2015 iMAC running HighSierra, i think the latest OS available for this iMAC is Monterey, I did the systems report to ID which products were 34 -bit and needed to be 64-bit prior to upgrade, and noticed that my Microsoft office software is 34-bit. I tried to upgrade to my Micrsosoft 365 so that I can upgrade the OS, but it states it needs OS12 or later which is newer than Monterey. Is my computer obsolete?