yeah, this is because SDL2 is such a pain library to use, i knew i regret choosing it i should've just used GLFW instead.
calculating delta time in SDL2 is bad, like you see how inaccurate the delta time displays in the debug menu.
i used SDL2 cause i wanted to "try out new libraries"... i regret it, i will switch to GLFW for this project and everything should stabilize.
in GLFW it is much easier to calculate deltaTime and it is much more stable, i will rewrite the game to be in GLFW, and at some point i will rewrite the game to use Vulkan too (or do something similar to my polygonal game engine and run both OpenGL and Vulkan)
edit: GLFW will also help very much with Vulkan it is so much good with Vulkan too