The origin of the fps drop can have multiple sources. Among these sources :
You have a laptop with two graphics cards and the game uses the smaller one.
A process that eats up the CPU in an abnormal way. This could be a Windows system process, an application, or malware.
CPU or graphics card overheating due to dirty or malfunctioning fans.
A problem on the graphics card due to out of date or incorrectly installed drivers. Hardware problems on the graphics card can also cause fps drops.
A software program with overlays of Teamviewer, Discord, GeForce Experience, and others.
In all these cases, please note that all your games should be slower than usual.
If only one of your games is impacted, as in this case, the problem may be related to the game itself, especially perhaps in the settings.
Also note that since the 1803 update of Windows 10, many Internet users complain about FPS drops.