Setting multisite in WAMP
I have never really used multi site much, but I have read the documentation multiple times nevertheless.

It always was my understanding that the default folder was reserved for the default site, and that all other folders should be placed next to it, not inside of it.

Next to that, the documentation implies that your folder name should match a certain pattern, based on the site url.

Instead of using www_d8multisite_com/sites/default/ms1 I'd try using www_d8multisite_com/sites/d8ms1.com instead.