This is a bit of a stab in the dark meat of the turkey, but the version of Windows you are running, 1909, has a limitation which causes performance issues in hardware accelerated applications (such as games, OBS and video players that use hardware accelerated decoding???) if multiple monitors with different refresh rates are present. Your system's monitors have 2 different refresh rates, 144 and 60, so you are affected by this limitation.
To fix this issue, we recommend updating to at least the Windows 10 May 2020 Update. Follow
these instructions if you're not sure how to update.
Also just generally recommended to run OBS as admin (I know you're not having issues with that) and strongly recommended that you record to MKV instead of MP4. You can remux to MP4 by selecting File > Remux Recordings in the main OBS Studio window or enabling Auto Remux in the Advanced settings.