Go to Device Manger ( control Panel > Hardware and sound> device manager)
In device manager
expand network adapters (if its not expanded)
Right Click on your network adapter that the computer is using ( ie wireless or Ethernet)
Goto its properties (bottom choice when you right click)
Goto power tab with in properties and uncheck allow this device to turn off
Then in the advance tab
Disable the following- (there is a box when you highlight them that says enabled or disabled make sure these are disabled)
Energy Efficient Ethernet
Green Ethernet
power save mode
and any other "power saving" names (every manufacture may use a different term) in that list of settings
Click ok.
Sometimes these cards Lock themselves into that powersave mode and will not provide more bandwidth. Microsoft sees this and disconnects thinking your trying to save power or its a slow Ethernet. They literally make software to test connections for Microsoft 365 (https://connectivity.office.com/)
.. so if they make it clearly low bandwith or slow ethernet (due to power saving and not waking up) is an issue. You don't realize it because it the computer was on this whole time but it was slowing the nic behind your back. its like putting your phone in powersave... some apps wont alert you if they have it programmed to not work with low power.
Same for microsoft.
also you can try to NOT allow your pc to goto sleep and or hybernate... as well which could be causing the issue. our office has all of our stuff on full max power 247. However anytime we have an outlook issue.. THESE settings were to blame. What good is green Ethernet if the software doesn't like it.