I have gladly linked you the exact specifications of the cable. https://www.delock.de/produkt/84928/merkmale.html

Yes, it's DP 1.4. Says so on the manufacturer page: https://www.delock.de/produkte/G_84928/merkmale.html And yes, it can handle HBR3, i.e. 3840 x 2160 @ 120 Hz in SDR without compression.

I have connected a pc monitor to a mac graphics card, I don't know for the imac if it works in monitor only mode

If the monitor has 4K resolution, i.e. 3840 × 2160 pixels, and the graphics card is fast enough. The cable is designed for 4K.