I find a part of the event with the noise floor to learn and split it. Right-click and use your Denoiser plugin and learn it. Escape out of that, and “undo” the splits. Now select the entire clip and process normally. It’s a pain, and I usually wind up custom labeling all my “to denoise” clips and going outside of Nuendo to process in RX. I overwrite the file (it’s usually a duplicate). You can always write new files with custom text and replace in your project from the pool. But with dozens of individual clips to process, this becomes cumbersome.