Why are my photos losing vibrancy when I switch from develop to library mode? They are also exporting this way. This has never happened before.
This is usually caused by a defective monitor profile.
As troubleshooting, and as a possible temporary fix, try setting the monitor profile to sRGB (or Adobe RGB if you have a wide gamut monitor).
If this fixes the issue, you should calibrate the monitor with a hardware calibrator as soon as possible, which will create a monitor profile that accurately describes your monitor.