Welcome,
@henry521 !
Post moved to a new thread.
On the topic itself, are you using a desktop or laptop?
1.) Very importantly, are you using any mods, or have you ever used any in the past?
2.) It's not uncommon for Windows updates to change power configuration settings back to their defaults after an update. Check both through Windows Power Config and your GPU Control Panel. Set everything to "Maximum Performance" (or something similar).
3.) 45 FPS sounds high enough that I don't think this is the case, but also make sure the game is using your RTX 2070, and not the onboard video. You should be able to force the RTX only through the GPU CP settings.
4.) If none of the above have any effect, try reinstalling DirectX and the Microsoft Redistributables that come with the installation package. (You should see a folder called "Redist" in the installation directory.)
Let us know how that goes!