i would like to know if it is possible to embed the pp3 when saving the output file (e.g. in a jpeg).
Imho it could be useful in order to be able to recover the profile used from the output image (think for example about web uploaded developed file, e.g. amazon prime photos or flickr: if some day i would like to change the raw therapee development and start from it, it would be enougth to download the image and load the embedded profile)
I don’t think that’s possible natively with RawTherapee.
If you’re on Windows you may be able to hack something together yourself with Powershell and NTFS alternate data streams. I can’t offer code, but just a line of investigation.