I have quite a few think tank lens cases for the larger lenses and the larger m mount ones like the 55-200m mount, but the smaller ones like the 15-45 size ones on their own are a bit small even for the smallest duo 5 size. so the question is what do you keep your smaller lenses in when going walk about.
I cant speak to small bags for the m series, but I got the old version of this Adorama Slinger back when I ordered my 5d2 many years ago. It works great for my 645 film kit, just the camera and a few lenses. Might not be a bad option to try a modest sling bag for the your M50. https://www.adorama.com/gbslbk.html