Windows 10 Laptop Slow only when on office network?

There is a laptop near me in which I have started experiencing a slowdown problem for a month ago.

My user says that it works fine at home, Starbucks, etc. but whenever he connects to our networks (via ethernet), it slows down considerably for an hour or more. He shuts it down daily, so updates are getting installed.

He says at the first time it happened only at the outlook, and it will take several seconds after clicking on a folder, email, etc. but before consecutive action would happen (folders would open email works, first-class)

He has a laptop of 32GB of RAM, and an M.2 drive (1TB), as well. and We have used 0365, so it’s not a hard drive/but it is a space issue.

After a long talk a few more questions raised and he said everything is affected by (other programs, internet, etc.). And he swears about this that this only happens whenever he connects to the office.

I have tried everything for what causes a computer had gone slow, and have changed settings to address that specifically (compacted emails, disabled graphics card accelerator turned off add-ins, disable startup programs, but there must be something I am missing because everything seems to point to the opposite to others (computers slow down when off the work network).

Are there any thoughts on this case which would be truly acknowledged.

Thanks a lot.