Darktable is for selecting a series of shots, going through them, developing the ones you want to keep.
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.
So perhaps closer to Photo Mechanic?
(Disclaimer: I may be biased).
Overall photo editing with open source software is kind of a drag. The features are more or less there, the UX isn't.
I wonder why the state of open source alternatives is so sad and what can be done to improve the situation.
I never used lightroom, so I don't know what I might be missing.
One thing that kept me from post-processing a lot of my pictures was the necessity of doing it on the desktop. I'd come back from holidays and didn't really make the time, I guess it can be attributed to laziness.
Nowadays however, I have a subscription for Lightroom and can import the photos on my iPad and edit them on the go, or from the comfort of my couch. I love it.
When I fire up Lightroom classic on the desktop, it downloads everything (originals) I've uploaded on the iPad from the Lightroom cloud. Although this has some inconveniences - it's just dumped into a folder without any regard for organisation - it prevents a complete vendor lock-in. Without that feature I wouldn't have considered this approach.
I love to take pictures, but post-processing is not exactly my favourite activity. I feel that all the tricks I used to get me to develop more on the desktop (e.g. getting a midi board for editing) didn't really get me anywhere, but the Adobe cloud + iPad just did the trick for me.
Search for "External Raw Import Tools as Plugins". I suggest you take a look at rawtherapee as well. I personally use both darktable and rawtherapee and find rawtherapee to be better suited for some usecases.