can i upgrade directly to the latest IS from Yosemite

No. Yosemite uses 32 bit apps ... Catalina and later use 64 bit apps.

Also, the various iMac models have limits in how far they can update.

How to: Identify your iMac model – Apple Support

NB: says: Models introduced in 2017 or later can run the latest version of macOS.

For older models, the latest compatible operating system is noted.

All the best :-)