Is isometric exercise good for muscle building?

Yes but has limits.: Isometric exercise, like weight lifting, etc. Can definitely build muscles, which helps capabilities/fitness, but is limited because it does not help cardiovascular health, and during the exercise, blood pressure can be greatly increased. This can be very disastrous in people who are vulnerable, like those with aneurisms.

Not very good: but... it sure can increase muscle tone. Stimulation of muscle that increases building is controversial and includes: damage from overwork lack of oxygen to muscle from overwork acidity/lactic acid in muscle from overwork hard to do with isometric. Also, not sure if it helps prevent muscle loss with dieting nor if it lowers risk of diabetes.