No, it is not possible to use the integrated GPU and graphics card together for the same task with this combination of hardware.
It is actually possible with some AMD APUs and graphics cards from about 10 years ago (called "Radeon dual graphics"), but it often didn't result in any increase in performance, because the latency penalty of communicating between the two GPUs usually exceeded the minor performance improvement from adding the extra performance of the integrated GPU to the graphics card. Games needed to be optimised to run on multiple GPUs in order to gain a significant amount of performance from dual graphics. I had an old laptop with 8650G + 8750M dual graphics, but most games actually ran better when dual graphics was disabled. AMD dropped support for dual graphics just a few years after introducing it, because very few game developers wanted to optimise for it.
However, it is sometimes possible to use an integrated GPU and graphics card for different tasks at the same time. For example, in some recording software, it is possible to use your graphics card to play a game, while using your integrated GPU to record and encode video of your gameplay. This can be useful for streamers and other content creators who want to ensure that all of their graphics card's bandwidth and computational power can be dedicated to running a game. An RX 6800 will typically lose about 5% of its gaming performance if you use its onboard video encoder at the same time.
