Push ups variation where you support your body on fingertips, does this variation actually build forearm strength ir is it mostly about pain tolerance to the skin being pressed by the sharp finger bones?
If you're strong enough to take them yes, but if you're not quite there yet, I wouldn't risk it. The stress you put on the small bones and joints in your fingers is immense.
As they are done on the fingers this is trained for the martial arts, it makes the fingers and bones in fingers very strong and hard.
In Kung fu they are trained to do push up on fingers and feast.
But it is very risky as it can damage fingers, which can result in a lot of pain.
These are one of the hardest and most advanced push-up varieties around. Basically, you're doing a regular push-up, but your palms are lifted off the ground and your weight is being supported on your finger pads. This takes an incredible amount of finger and forearm strength, but you can work up to it by doing short plank holds on your fingertips.