I am using a STM32F413ZH-based custom board, I was looking into the option of GUI applications and found TouchGFX. But I don't know how to use that and integrate it with my custom board. Please tell me how to integrate TouchGFX on my STM32F413ZH-based custom board. If it can't be used, then let me know about any other applications.
One option is to install TouchGfx Designer and look at the supported boards, then you can develop what you need on these and continue with your own design. There is a series of STM32 Discovery boards supported. For example the STM32F429I has 240 x 320. There are also references on the internet how to port TouchGfx to ILI9341 based boards typically supporting 240 x 320. If I was you and wanted to go the GFX path, I would first invest in a SM32F429I, make this work and then continue. The code generated by TouchGfx can be compiled with STM32Cube IDE and then downloaded to these boards without much problems.
All these things are so very much the same, find something close, and pivot slightly.
Cherry pick amongst what is available, get a broad outline of what you need, and then do the fine finish work to plumb things together. Find data sheets for other parts, and look for drivers and frameworks from other sources, and port or modify to fit STM32, most everything is available in C on some platform or another.
ST is only developing code/drivers for things they themselves ship, so don't expect all the pieces to be prebuilt (LEGO). They had suggested some market place for software components, but nobody is willing to pay for anything, so I'd assume that's why that went nowhere.
It would be acceptable to do that if there were some plain english cookbook style instructions on how to do some of the very things being asked here. Many of the application notes not only leave out some infinitesimal critical details, but lack explanation of how things are structured enough to make deducing those critical details neigh impossible.
STemWin is one such example, and I haven't bothered to look deeply into TouchGFX...