I have spent the last few weeks trying to find a solution for Apple's elimination from Photos (with no prior notice or warning to its user base) of the retouch tool. I thought that it might be helpful for me to share with the community what I have explored and what has and hasn't worked. Unfortunately, I have yet to find an acceptable solution. It would be helpful it other folks could share what potential solutions they have investigated.
The most extreme solution is to switch to an alternative photo editing and storage solution like Lightroom. I signed up for a free 7 day trial of Lightroom. I had experimented with Lightroom years ago so I was some what familiar with the product. There is a huge learning curve. However, one problem is that Lightroom is now cloud based and you have to store your images on Adobe's servers. That's a non-starter for me. Adobe does still sell Lightroom Classic as a stand alone product, but it is clunky and out of date and feels like an end of life product. However, the biggest problem with switching to Lightroom (or another Adobe product like Photoshop) is that it appears that alterations to images made in Lightroom (or Photoshop) will not transfer to Photos and vice versa. Thus, Lightroom is not a viable solution unless you are only going to use it for new images and do not intend to import images altered in Lightroom (or Photoshop) into Photos.
I next tried Affinity, which is a reasonably priced editor that does not include a library/organization component like Photos or Lightroom. Once installed, you can access Affinity in Photos in the Edit window and edit an image in your Photos library using Affinity's editing tools. Again, there is a huge learning curve. But the real problem is that it appears that you cannot make additional edits to images previously edited in Photos. You have to start from scratch with the original unedited version. (I plan to contact Affinity support to see if there is a work around but have not yet had the time to do so). So, Affinity does not appear to be a great solution either for those of us who simply want to retouch an image outside of Photos but to continue storing the image in Photos and retouching the image outside of Photos while retaining all prior Photos edits. Apparently, there used to be a separate "retouch" Affinity plug-in that worked in this manner but it appears that it no longer works with the current version of Photos. If anyone has any experience with this plug-in, it would be helpful if you could post it.
Since I have yet to find an acceptable solution, I am currently editing new images in the pre-15.1 version of Photos running on an older Mac and then importing them into the Photos library on my Studio.
I will continue to investigate potential solutions and will share my findings. Since it appears that Apple has no intention of restoring the retouch tool, those of us who would like to continue storing images in Photos need to find a replacement for the retouch tool. There must a a solution out there somewhere. We just need to find it.