Increasing VRAM in an Intel 5K 2020 iMac

Note that new external GPU enclosures and all-in-one external GPU boxes can be quite expensive. The enclosures that I saw on the OWC and SonnetTech sites went for $400 – $600 USD. Throw in the cost of a high-end graphics card to put in an enclosure and it might not make sense to go that route.

Use an external graphics processor with your Mac - Apple Support

Use Blackmagic eGPU with your Mac - Apple Support

The GPU (AMD Radeon Pro) and its VRAM are soldered directly onto the logic board. There is no way to upgrade them internally via software or hardware.

You cannot upgrade the video memory, but you can easily upgrade the system RAM up to 128 GB via the physical hatch on the back of the iMac.

Since this is an Intel-based iMac, it natively supports External GPUs (eGPU) via Thunderbolt 3. If you need more VRAM for rendering or video editing, you can connect an external enclosure with a compatible AMD Radeon graphics card to bypass the internal GPU limits.

I believe that Apple officially supported eGPUs on Intel through macOS Ventura, but not afterwards on Intel and not on any Apple Silicon Macs (M1 - M5).