How do I connect external speakers to an iMac via Thunderbolt?

think the older intel imacs have the 3.5mm minijack headset connector on the back

it's the round hole with the headset icon on it https://billeder.dba.dk/dba/914a8da0-1638-48b4-be58-cf515dc59393.jpeg?class=S1600X1600

if it's the new arm cpu imac then it's on the side https://help.apple.com/assets/6244BE6AE83C5279F505C060/6244BE75E83C5279F505C0C5/en_US/f95b4d6a3c555233568e5dbfa24ebc2f.png

if you want to connect it to usb-c then it will be an external audio card bypassing the audio system of the imac, that path would cost more

The technical specifications for the 24" M1 iMac indicate that all versions have two USB4 (Thunderbolt) ports and a 3.5mm headphone jack. Sounds like the headphone jack is all you need for your Logitech speaker system.

It's the two USB-A ports and the Gigabit Ethernet port that Apple leaves off the cheapest model.

iMac 24-inch - Technical Specifications - Apple

I could be wrong, but I though that they all had a headphone jack on the side.

If not, then you need a USB-C to Audio adapter.

for examples > https://www.google.com/search?q=usb-c+to+audio+adapter

What speaker system do you have?

(brand, model and connections)

You should just plug the Logitech Speaker System into the new iMac’s Headphone jack.

In case you missed it, the new iMac’s headphone jack is on the lower left side.