Demand for responsive theme getting more and more desirable especially now that Google is now using it as a "signal"
"...mobile-friendliness is now considered as a Google Search ranking signal"
grep is your friend.
Vanilla passes Google's mobile friendly test out of the box (at least, my forum did...)
This is the result of the test using the link above.
You must have got a different result than me then.
The only problem with the mobile theme here are some link background colors which make the add on linked on the discussions list not be readable even with glasses. Just a bad color combo, but other than that it works ok... most of the time because sometimes I get the full site instead and have to make it bigger to be able to read. And the add on section also bugs out... I can't see how anyone would want to use a phone to participate in discussions or to blog, it is so cumbersome...tiny screen limited options..
Nevertheless , I tested my own forums which use my mobile themes and they all passed ... So the issue must be with the theme or the content of the particular site at that time if you get a fail.
Mobile friendly means easy to read in a tiny screen, all you need are big letters...
❌ ✊ ♥. ¸. ••. ¸♥¸. ••. ¸♥ ✊ ❌
2/2 for me!