Hallo Unmesh,

opto in linear mode gives you an anolog signal with opto isolation.
Whether your idea with optocoupler and VCF is good depends on your needs. If you try to monitor fast changes of your current, use of VCF might be to slowly, perhaps. So, tell us what you actualy want to measure, and what you want to to with the result. Only monitoring, or something like overrating protection...

We additionally need to know, how your 900V power supply is fabricated. Is their any connection to your system ground (0V of mcu circuit)?

By the way, 2000A, is this a typing error? 2000A with 900Vdc would give a power consumption of 1.8million watts. Is that true? Also, your shunt would have to dissipate 75mV x 2000V = 150W. Is that true?

Bye,
Kai