Everytime I do ghsul for janaabat I sit in the bathtub and keep repeating the niyyat in my heart and it take me around an a hour to be fully satisfied with my niyyat... (I think I'm kind of having OCD idk) so can I leave niyyat and just start with bismillah and carry on with ghsul as usual. When I'm done my brain it's so stressed. Please answer me I need the answer very urgent
Niyyat(Intention) is a must. Every single work is based on intention.
I heard Allah's Messenger (ﷺ) saying, "The reward of deeds depends upon the intentions and every person will get the reward according to what he has intended. So whoever emigrated for worldly benefits or for a woman to marry, his emigration was for what he emigrated for."
Sahih al Bukhari 01
So if you do a work the results will be based on your intention. If you want to take bath for cooling you then that is not the ghusl of janaabat. If your intention is the you would do ghusl for janaabat and to become pure again then that ghusl will be valid and you will be pure.
Your problem is you keep thinking about your intention. You don’t need to keep thinking about it. If you had your intention that “I will do ghusl to remove impurities and become pure and pray again”. That is enough. Afterwards you follow the rules of ghusl and complete your ghusl.
The majority view is that niyyah is required for ghusl, as without it one wouldn't be tahir and therefore the minimum condition for praying is not reached.
"The reward of deeds depends upon the intentions and every person will get the reward according to what he has intended. So whoever emigrated for worldly benefits or for a woman to marry, his emigration was for what he emigrated for."
(Different quotations and versions in Sahih al-Bukhari 1, 2, 3, 4, 5 Sunan abi Dawod, Sunan ibn Majah, Imam Ahmads al-Musnad)
However the hanafis don't consider it as essential for the validity of ghusl. This was also the view of Sufyan at-Thawry both say that ghusl and wudu' themselves are no pure worship and only a pure worship like the prayer requires an intention.
Further be aware that matter of niyyah is very simple it is achieved if one had in mind to do an act (however some scholars would require a niyyah taking place at the moment one starts the act itself).
This fatwa -in Arabic- on islamweb #13029 discusses the differences of opinion among scholars about (obligatory) acts related to ghusl.
You shouldn't complicate things.
As long as if someone suddenly out of no where just jumps at you and asks what are you doing and you're answer is I'm making a ghusl then you're good ie you're not asking yourself "Did I just make ghusl...funny I didn't know how that happened. I just wanted to wash my foot. I didn't want to make a ghusl. "
The only timeethat won't happen is (and this happens more often with wudu) is if say you'r on the phone and decide to wash your hands, and for no reason and merely a force of habit you just make a wudu, I mean you don't even have an intention of purifying your soul, you just do it automatically and at the end of your wudu you'r surprised that you actually did a wudu...
Such a wudu is not accepted.
However if you were on the phone and talking to someone but also needed to quickly make wudu for your prayer to catch the plane and decided to just make wudu while on the telephone then you're good. You're good because you made a sane decision about making wudu.