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

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.

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.