As there are so many videos on OBS, and I don't exactly know what you've watched, tried, or what your settings are at, I'm going to start from ground zero. Sharing logs really help diagnose problems, and you have not provided any. If anything try to duplicate the screenshots I provide below for further help.
In Windows... You want this.
In Windows... You DON'T want this! Make sure these are all at 100.
With OBS you can actually have your speakers turned all the way down.
These are the settings I use and I can record just fine.
Setting/Audio tab: I just have my Desktop Audio set to "Default". (My mic is not currently plugged in as it shows here.)
In the mixer window, go to Desktop Audio. Hit the gear icon, then select "Advanced Audio Properties".
Have Audio Monitoring OFF, and select at least Track 1 for both Mic & Desktop Audio. This window is also handy if you wish adjust volume by percentage instead of using the slider bars for making adjustments.