Does my iMac have a dedicated or integrated Graphics Card?

iMacs go back a long time. Many PowerPC-based and Intel-based ones had discrete GPUs. I believe that all of the 27" iMacs did. It appears that starting in 2013, non-Retina 21.5" iMacs had just integrated GPUs. (When 4K Retina screens came out, discrete GPUs reappeared in the 21.5" iMac line.)

You can find more specific details in MacTracker, in archived Technical Specifications on the Apple site, or at some Web sites that keep track of old Mac models.

All Apple Silicon processors have integrated GPUs – Apple designs these processors as "System on a Chip" (SoC) units. In the Intel/AMD world, people have traditionally associated integrated GPUs with lower performance. The higher-end Apple Silicon processors are designed to provide a lot of RAM-to-SoC bandwidth, so a M1/M2/M3 Max chip might deliver GPU performance that – in the Intel/AMD world – would involve a discrete GPU.

This article is about the older M1-series chips, but you might find it an interesting read.

AnandTech – Apple's M1 Pro, M1 Max SoCs Investigated: New Performance and Efficiency Heights

The iMac GPU is integrated into the Apple Silicon chip architecture.

See the section about the Chip, not far from the top of this doc:

iMac - Technical Specifications - Apple

Yup, integrated, been that way since 2012.