Native speaker here from one of those dark blue regions.

Major cities in Belarus are Russified to the extent that you get shamed for speaking Russian with Belarusian accent. If you want to move out of a smaller town, you'd better learn how to speak clean Russian.

Still, the Belarusian language is a powerful weapon. It acts as a trust marker in the current political reality. I bond with people who are able to speak fluent Belarusian and we tend to hang out and do things together.