There are many factors that influence the drop in performance. The first one identified is the particle system, in the game I use about 1,000 particles that the emitter activates under certain circumstances, but apparently even if the emitter does not start, those particles affect the performance, just by putting 1000 particles in the emitter without it starting.
In this image the emitter is at 250 particles, and I have removed the rocks.
Translated with www.DeepL.com/Translator (free version)