How many mountain bikes are sold today with the ability to trim their front derailleur? In light of that, are there any truly micro-index shifters available where you can dial in enough movement to shift from one ring to the other and then dial up/back as needed to keep it from rubbing? I sort of saw a prototype at Walmart when one of their display models was incorrectly installed with the right 8-speed shifter mounted to adjust the chainrings

https://www.paulcomp.com/shop/compon...imanothumbies/

since the trend is for bike shop level MTBs to be 1x, I would say the % with a front derailleur to even trim is quite small. Its mostly a moot issue right now. But there are still some with 2x and 3x, so FDs obviously exist.

My old MTB that was 3x9 could trim up front. There was a dead shift, effectively as that trimmed the FD depending on where the chain was on the cassette. That was with lowly Alivio shifters even.
The only micro indexing shifters for MTB would not be indexing at all. They would be friction like what was already linked.

SRAM grip shifters have about a dozen clicks on the left.

Thumbshifters have front trim; Suntour types have a front microratchet. I believe Sunrace and Microshift make modern ones.

They don't come on many new bikes, and are difficult to mate with hydraulic brake levers in my experience, but I haven't tried the new Magura levers

But then, how many mountain bikes these days have a front derailleur?

They used to put the indexing left shifters on and I always swapped for the "friction" type with the dozen or so clicks. Trimming is a breeze with that.

The SRAM ones I've seen with three clicks were from their early heyday in the late 1990's. The more recent I've handled have about a dozen. I don't know if that's true of all. It sure does make things easier.