What is the ruling on an architect working on a tourist hotel project that contains forbidden things, and the salary earned from it, and is it permissible to leave this job and join another lawful one with a lower salary?

The project you mentioned contains both permissible and forbidden benefits. Therefore, it is not permissible for you to execute or follow up on the forbidden matters, and the salary corresponding to them is not lawful. There is no objection to working on the other permissible tasks within this project. However, it is advisable to transition to a purely lawful job, even if its salary is lower, for whoever abandons something for the sake of Allah, Allah will compensate him with something better, as stated in the Almighty's words: "And whoever fears Allah - He will make for him a way out And will provide for him from where he does not expect" [Quran 65:2-3], and according to the Prophet's (PBUH) saying: "Indeed, you will not abandon anything seeking Allah's pleasure except that He will give you something better than it."