connect firewire device to USB port

The V700 has a USB 2.0 port. Use that instead of the Firewire port. You will need a USB-C to USB-A adapter like this one:

USB-C to USB Adapter - Apple

You will also need an ordinary USB cable to connect the adapter to your scanner.

Of course if you absolutely want Firewire, you can go the complicated & expensive route and use all three of these adapters to connect via Firewire:

• Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple
• Apple Thunderbolt to FireWire Adapter - Apple
• FW800 to FW400 adapter cable

Not easily.

Firewire and USB are fundamentally incompatible.

You may be able to get it to work using a Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple and a Apple Thunderbolt to FireWire Adapter - Apple

If the scanner uses firewire 400, you will need an additional firewire 400 to firewire 800 adapter.

New iMac->USB-C to Thunderbolt 2 > Thunderbolt 2 to FireWire (800) >Scanner

There comes a time when updating hardware is necessary though.

What model is the Epson scanner?

It should have a USB cable with a larger USB-A connector to plug into a computer.

If that is what you have, then you would just need a USB-A to USB- C adapter to plug it into the new iMac.

There should be some adapters available, or even cables from FireWire to USB

But be cautious because there's two Firewire versions: 400 and 800

If you won't be able to find for USB-C (assume You won't) -- an extra dongle would be necessary (to have classy USB to connect)

So, if will look like: Mac's USB-C (or Thunderbolt) -- Dongle for USB -- adapter Firewire to USB -- Scanner

Ptaxey wrote:

There should be some adapters available, or even cables from FireWire to USB

No. There are no real cables that go directly from Firewire to USB because the are fundamentally incompatible.

That model appears to have a USB 2.0 port. In which case you can use that with a USB to USB-C adapter and a regular USB-B to USB-A cable.

Link-> https://epson.com/For-Work/Scanners/Photo-and-Graphics/Epson-Perfection-V700-Photo/p/B11B178011

Link-> Syntech USB C to USB Adapter Pack of 2 USB C Male to USB3 Female Adapter Compatible with MacBook Pro 2021 iMac iPad Mini 6/Pro MacBook Air 2022 and Other Type C or Thunderbolt 4/3 Devices Space Grey - Amazon.com

Link-> UGREEN USB Printer / Scanner Cable - USB A to B Cable, 2.0 USB B Cable High-Speed Printer Cord Compatible with Hp, Canon, Brother, Samsung, Dell, Epson, Lexmark, Xerox, Piano, Dac, and More 5 FT

There is no such thing as a Firewire-to-USB adapter or cable. Anything you can find on AMZ, eBay and other vendors that says they do are all a waste of money and will not work, FW & USB are not compatible and I have never seen a working FW-to-USB adapter.

I agree with Phil124.

Ditch using the scanners FireWire connection and dig out or get a USB-B to USB-A cable and a USB-A to USB-C adapter.