It has been officially end-of-lifed by ESRI in favor of the Office365 type plugins, sadly. I can't even find an old one hanging around anywhere.
Last filename I had was:
"ArcGISMapsForOffice_x64_2020.1.1_en" for 64-bit Excel, there was a companion for 32-bit as well.
Some scammy-looking d/l sites seem to have it, but who knows what they really are?