iMac 2019 no thunderbolt

Thunderbolt 3, which your 2019 iMac has, uses the USB-C connection. This is a change from the prior versions of Thunderbolt. To obtain the maximum speed of 40Gbs, you’ll need to use Thunderbolt certified cables and devices such as SSD drives the support the higher speeds of Thunderbolt 3.

Hi, welcome to the Apple Users Community.

Please try this link for help and information on Thunderbolt 3/USB C

https://support.apple.com/en-us/HT208368

There are limits on how long these cables can be and work effectively but they are significantly faster than USB-3. The other bonus is unlike the USB 1, 2, 3 style connector you will never mistakenly try to insert the connector upside down and be wrong.

Best of luck