Industrial networking resources? Who is the leading standard for OT leaning from an IT prospective?

I just recently started working for a processing plant/OT network and would like to learn the foundations of it. There seems to be a convergence between the two happening as a current trend. I wanted to take the Cisco Industrial Networking Specialist cert but it has be retired.

I cannot find any training resources on this. For anyone IT administraros in the field of OT/Scada, what are good resources for me? Is there a standard certification for OT learning from an IT perspective?

Thanks