Anyone know if masks are mandatory in Bangalore? Is there a government-issued order on this?

I don't know if the government is enforcing or not. Most of the public places like Grocery shops, medical stores, are voluntarily enforcing the wearing of mask. They are not allowing you to purchase if you don't have a mask. I think it will be the case for all the places in future.

Turns out that there is a govt order to enforce masks in BLR now: https://timesofindia.indiatimes.com/city/bengaluru/karnataka-government-makes-wearing-masks-in-public-mandatory/articleshow/75055464.cms