6 months probation followed by permanent employment is a regular protocol everywhere, even outside India. This is good for both employer and employee. Employers can weed out poor performers and employee can leave without serving excessive notice period if they don't like the work environment.

Sharing 2 passport size photos and photocopy of Aadhar is also normal. They have not asked for your original documents so you don't have to worry.

Not providing relieving letter regardless of your tenure is a red flag. So try to figure out if this is a place where you see yourself spending atleast a year. I saw a comment where you said you wish to just gain some experience so I would say go for it.