Hello to all the guys and gals out there, "sorry this is a long answer"
I have sympathy for all the people who struggle with muting either the d or b string or in fact any string, I have the same prob on "some" guitars,,
I was extremely frustrated so decided to do a simple study, I read all the articles and advice from people saying press harder ,build up strength, roll your finger etc etc,, I had been an bricklayers hod carrier for years and could hold solid concrete blocks between my thumb and fingers, but still had probs on the guitar, It is was my finger shape that is the problem, the creases fell naturally over the D and B and even twisting the finger did not help as the crease go's a certain amount around the side, I even tried over a couple of years to adjust my finger back and to but this was not natural to me and it also brings forth other problems, So I looked at various guitars I now have 15, some I mute the strings Some I dont,, WHY!, It is the shape of the fret board, Guitars with smaller radius are much better for instance 12 and below are fine, anything above was a problem, you see some people have a natural curve in their index finger and that coupled with the fact the crease is quite deep and falls naturally on D or B string or in fact any string will cause the problem. I proved this to my self by playing an ibanez with a compound radius ( flatter as you go up the arm ) no problem with barres near the headstock but higher up where it is flatter YES problem, I have no problem playing my Strat, Tele, or Rickenbacker ( very small radius ) Some acoustics have a small radius, My Ovation celebrity has a small radius.
I have just started to teach my Granddaughter to play, She can barre my flatter guitars better than me, her fingers are straight and have virtually no crease, my hand and grip is 10 times stronger than hers, so my advice is try some guitars at a shop, also try ones with jumbo or semi jumbo frets because this also really helps,, cheers every one