Ran into this when going to make jam sandwiches, intuitively I should be able to use a jar with no lid and have it not be sealed for when I'm immediately using the jam rather than wasting a lid that isn't needed.

Based on changes since 3.2.2 it doesn't look like this has been added, if it has the github pages page for jam is out of date.

We use the issue tracker exclusively for bug reports, not suggestions or support requests. To which I believe I've already answered you.

There is no obvious place to make suggestions, and simply going "not planned" doesn't explain why when TFC is supposed to be aiming for a "believable" experience (jars are obviously filled before being lidded).

There is no obvious place to make suggestion

There's a channel named #suggestions... As I've already said, this is not the space to debate them.