How can I concentrate in studies over 4hour+?

A good night of sleep, stay hydrated (aka don't drink more than 2 coffees 😆), whatever you study, divide your tasks into sub-tasks so you see your progress, and quite frankly... take breaks!

take breaks and do time boxing

you can find playlists on youtube. Music really does help. Also having a calm and quite environment

I'd suggest study in chunks, instead of 4 hours straight

Yes, you can - with good music, high speed internet, quiet space, 20-25 oC and a computer. Everything is possible.

Changing subject focus every hour