Is it allowed to drill this part to install a tv bracket? If not allowed, is there another way to mount the tv there?

columns and beams cannot drill through. but i don't think it's an issue to drill up to 50mm deep since columns are RC which are similar to household shelters and HS rule is drill no more than 50mm deep.

but are you sure you want to place the TV next to a window? you may encounter very bad glare from the light outside.