There's no need to downgrade R when you adjust the RTermPath setting in Zorro.ini or simply install/update R in a default directory minus the version number, 'C:\Program Files\R\' in my case. Then you only need to adjust the RTermPath path once. Make sure you backup Zorro.ini as it will be overwritten when you install a Zorro update.
I use R 4.2.1
I only use a CPU for processing, so I can't help you with your GPU issue.
I believe the R version does not matter, but a new R installation could solve issue with incompable Keras and Tensorflow versions. We found that when Tensorflow or Anaconda was already installed on a PC, Keras just uses the installed versions regardless whether they match or not. That was probably the reason for the issue.
When you train with the GPU, disable multiple cores. PCs have multiple cores but normally only 1 GPU. There can be also other restrictions with GPU training.