I have to activate MS Office 2021 every time I open Excel, Word or PowerPoint

Office 2021 for Mac requires the build 16.53 or later to use the Universal2 binary support, allowing it to run native on Apple Silicon Macs with Big Sur or later. Update Office 2021 for Mac to the 16.53 build or later. Microsoft 365 has been a Universal2 binary distribution since v16.44 in Dec. 2020.

It is not compatible with Big Sur and I have to run it with Rosetta.

It is the M1 chip that it is not compatible with. It’s been well over a year since M1 Macs were introduced and longer since all the other software developers were advised about them so I have no idea why Microsoft couldn’t put out a universal app, but they put out a 32 bit app five years after Apple announced full 64 bit.

I also have to activate it every time I open one of the apps.

you should contact Microsoft support. They have a license reset tool they should be able to provide you with in order to reset your license but I’m not sure that that is what is wrong.

Apple doesn’t manage their licensing scheme. I’m running 2019 on an M1 Mac and it doesn’t constantly ask for activation, so it is something with their license management that isn’t writing the data.

Office 2016 works fine (although no longer have MS support). Seems like Office 2021 should work. I have it on both M1 and Intel Mac.