Darktable is for selecting a series of shots, going through them, developing the ones you want to keep.
So perhaps closer to Photo Mechanic?
It's nowhere near as polished as Photos, but it's capable, open source, and multi-platform. I hope to maintain my photo library for decades, so avoiding proprietary software / service lock-in was my most important consideration. This decision was reinforced earlier this year when we had to do some surgery on my spouse's meticulously curated Photos library: it's damned near impossible to completely preserve metadata when moving items between Photos libraries, and it is impossible to remove RAW files from stacked RAW+JPEG pairs in the Photos library. If I ever ran into those issues in digiKam (which I haven't), I'm confident that my SQL abilities would be sufficient to work around them.