MU-plugin to set 'Site Identity Favicon' across all Multi-sites

For quite a few reasons I am having difficulties with 'stabilizing' a generic 'Site Identity Favicon' across the browsers of my multi-sites (mostly because all sites have individual admins!, who change & delete things at will!)!!!
My assessment is that to set a universal 'Site Identity Favicon' via code (in a theme function file or a 'must use plugin') would be the way to go!
I note "Method Four" on the resource:-

Is a Mu-plugin possible, please?

Could anyone advise me please?

Thanking you in advance.