so I copied an old blend file and started working on a new animation, but the frame rate changed from the original 75 to 30. I changed it back and made the animation but the framerate still runs in 30-40 even though the first animation still runs in 75. The dope sheet even says it's running in 30. The full video below shows the issue. https://drive.google.com/file/d/1xTYVp6GbZv1kzQ_io2dKH_tobEmSQ02q/view?usp=sharing
The framerate shown in the 3D view Window is the maximum framerate your hardware can achieve trying to animate your mesh at the programmed framerate. If you render the scene it will be rendered at the expected framerate (the setting in the properties panel), but during realtime play, if the complexity of the scene reaches the limits of your hardware, the animation gets slowed down, and the info on the 3D window tells you how much.
If you want to see your animation in real time at the desired framerate, you have to temporarely simplify your scene (turn off unuseful pieces and/or create simplified proxys of your meshes), or boost the qualities of your hardware. After the animation is finished you can switch back to the original meshes for rendering or exporting.
These are areas in which others specialized 3d softwares (Unreal engine, Unity, ...) shine better than Blender.