Need help transferring files from my old iMac (mid 2011) to my brand new iMac (2020)

2 cables...

https://www.apple.com/shop/product/MMEL2AM/A/thunderbolt-3-usb-c-to-thunderbolt-2-adapter?afid=p238%7CsXJVdwN9q-dc_mtid_1870765e38482_pcrid_246386725857_pgrid_14874603490_&cid=aos-us-kwgo-pla-btb--slid---product-MMEL2AM/A

https://www.bhphotovideo.com/c/product/1139474-REG/apple_md862ll_a_thunderbolt_cable_1_6.html/?ap=y&ap=y&smp=y&smp=y&lsft=BI%3A514

Migrating is incredibly simple. The fastest and most reliable method is to connect the old iMac Time Machine external HD to the new computer using a USB cable. If you have not turned on the new computer for the first time, this is the easiest method. When you turn on the computer the first time it will launch Setup Assistant (SA). SA will get to a point where it asks if you are migrating from another Mac, select Yes and follow the on-screen prompts.

If you have already turned on the new computer and completed SA. Then connect the old computer TM EHD and launch Migration Assistant (Application -Utilities - Migration Assistant) and follow the on-screen prompts.

NEVER use wi-fi and I strongly recommend against using an Ethernet cable. Using the old computer's Time Machine drive is tried, true and it just works.

You connect the old Mac's Time Machine external HD to the new computer using a USB cable and run Migration Assistant. If you backed up the old computer using Carbon Copy Cloner or SuperDuper! either of those will work too.

If you don't back up, that is BAD and certain guarantee of lost data. At the very least you should be using Time Machine.

Fairly certain, but since they haven't issued any 2020 iMacs yet I assumed yours was a 2019 iMac with Thunderbolt 3, and also that your 2011 iMac is a 2011 iMac with Thunderbolt 1 port.

Great news, you're welcome & take care my friend. :)

You don't need to connect to the old Mac at all, all you need is it's Time Machine External Hard Disk.

Did you have an external Time Machine Drive on the old one? That could be connected to the new computer.

Then you're stuck with Target Disk Mode & the expensive cables.