[2021] Did the targeting of the Soil Sampler get changed/fixed?

I've just tried to reproduce that and it works fine here, you need a bit targeting skill (nothing has changed there), but it works without hassle. Are you maybe having issues because you have planted many saplings directly next to each other making it hard? That will no longer be possible in 9.5, so you might want to adapt for that already.

You need to aim at the ground, yes. That did work for me, though. It was never possible or at least intended to be able to point on trees, so if that worked for you, I have honestly no idea why.

The minimum amount of emtpy blocks between saplings in 9.5 is currently equal to world generation, 4 blocks. I don't think the soil sampler will be changed to allow targeting the plant, basically as it's intended to measure the soil, but I'll note it down for consideration :)

We do plan to introduce a global modifier, yes. I do not have an ETA for that, though.