film scanner compatible with iMac Ventura

Have you tried the VueScan app? When my old Canon scanner no longer was compatible when I upgraded to Catalina I tired it and it worked beautifully. There's a demo version you can try before purchasing.

What Nikon scanner model and what is the cable used? Most Nikon scanners are supported by the paid (free trial) VueScan Professional scanning software if you can sort the cabling and adapter for new iMac. Scroll down on that link to see the supported models.

When Hamrick was creating VueScan, they had a participating Nikon dealer that kept them supplied with new Nikon scanners which they used to provide early Nikon scanner support into their scanning product.

I too am trying to use my old Nikon Super Cool Scan 4000 with my M1 mini but am still at the "what cable" step as my scanner has the 6 pin Firewire. So I am ordering some inexpensive adapters SKYPIA New Firewire IEEE 1394 6 Pin Female F to USB M Male Adaptor Converter in hope that will work although I will not be able to use my Thunderbolt 4 USB-C, and will have to use the slower USB. Then on to scanner software. Anyone else's experiences appreciated.

VueScan Professional has supported the Nikon Super CoolScan 4000 since it was first introduced by Nikon.

Sounds like you may have the cabling/adapter part solved. VueScan will let you know if it detects the scanner.

The PlusTek OpticFilm 135i is supposed to be compatible. I would check with the vendor to be sure.