Since no one else seems to actually be answering you, I’ll give you one. Smart Objects AKA linked layers. I use these in just about every single PSD and it has saved me rediculous amounts of time and effort undoing or redoing edits and avoiding destruction of a raster image by rotating or scaling it multiple times.
There has been a feature request open for this for 10 years and it is still not implemented. I first found out about the intention to add linked layers several years ago but I quickly gave up when I realised how much time it was taking.
I couldn’t tell you other features as I have not used Gimp much beyond trying it out for some light projects and to make use of some of it’s better-than-Photoshop color to alpha tools. But this one feature combined with all the UI, behaviour, and shortcut decisions is enough to keep me stuck on Photoshop for Windows for a long while yet.