Thanks for the info.
I finally found the exe.
It's actually called WebViewHost.exe & it sits in C:\Program Files\WindowsApps\Microsoft.MicrosoftOfficeHub & a following bunch of alphanumerics. So its a protected hidden file, that I can unhide, & even with admin permission, I cannot get into the WindowsApps folder.
I have an Asus A15 Rysen 7 laptop with an RTX3050 GPU. What I wanted to do was to use Office 365 with that card, instead of the default onboard graphics.
It should be possible to set the RTX GPU as the default GPU, but you cannot. you can only (in Windows settings, Display) set a program/game etc to use the card. So, based on the location of WebViewHost.exe, I cannot get the RTX GPU to access it.
Bit of a head scratching to find this info...