I want a thunderbolt cable to suport my 2020 mac to my 2014 mac. the ports are diffrent

Even with the Thunderbolt adapter and Thunderbolt cable, a 2020 iMac cannot use a 2014 iMac as a display.

Use your iMac as a display with target display mode - Apple Support

"You can connect any of these older iMac models to another Mac from 2019 or earlier for use as an external display."

You meant to need "male-to-male cable" between Thunderbolt 2 iMac and Thunderbolt 3 iMac.

That you will need

1. Thunderbolt 2 cable male-to-male -- 0.5m or 2m (just use drop down menu to choose the length)

2. Thunderbolt 2 (female) to Thunderbolt 3 (male) cable

Extra note:

If you want to transfer files, probably, using network will save you some money. Personally, I really do not see the need to connect both iMacs together. Or, you can use TimeMachine to restore everything from old iMac to new one.

You also can set up share folder, to transfer needed files in between.

https://www.apple.com/shop/product/MMEL2AM/A/thunderbolt-3-usb-c-to-thunderbolt-2-adapter?fnode=93b2ec3e0ad9d9ecb13a568d2d52b508c8c11c0f8f9b065e9940855b49f702218141250cf1648036da6b5c9e74e59c0852a48469497b22a6343c0b104957798d3d54eb0f8fde95a979d98cf440b1de932d9b8744e50c7763c58417102207dba9f55ae66d91bee5c759df6ba591a0f012