What kind of cable do I need to connect my 2010 iMac to the new 2021 24inch iMac to transfer my data over.

The Migration Assistant app was created to assist with these transfers. Whichever way you choose to do it, I would only recommend connecting the two computers with a USB cable. Quick and easy to do. Using i-Fi is very likely to cause data corruption because it is too slow for this much data.

It looks like 3 or 4 cables...

https://www.apple.com/shop/product/MD464LL/A/apple-thunderbolt-to-firewire-adapter

https://www.amazon.com/Apple-Thunderbolt-USB-C-Adapter/dp/B01MQ26QIY/ref=asc_df_B01MQ26QIY/?tag=hyprod-20&linkCode=df0&hvadid=309881068962&hvpos=&hvnetw=g&hvrand=4616556342846018417&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032541&hvtargid=pla-439937624856&psc=1

And a FW800 cable & a Thunderbolt cable.

Much cheaper & easier to connect an External drive to the 2010 Mac to do a Time Machine Backup, then just move the drive over.