Changing just the misleading title
If nothing else looks wrong and the change in title helps then it is probably not too minor. But if there are other things that look wrong at a quick glance reject as too minor. If you see only 1 or 2 things that could be fixed click improve instead.
Editing formatting of menu options from
backticks to emphasis
Back ticks are not for emphasis. They are meant to be used for inline code. If all they are doing is adding emphasis. I would reject as too minor. And too many code blocks can make the readability worse.
Adding formatting to file paths to improve readability
Do you actually think it improves readability I would say it might be ok. However if you are unsure skip.
Fixing some problems in a low-quality post that will probably be removed
When looking at suggested edits don't think about them as if they are going to be removed in the future. Think about them more as does this edit make the post better now. If the edit fixes most of the problems in the post accept it. If it fixes some either reject as too minor or improve it yourself if you think you can. Or just skip it if you do not think you can accurately judge the question.
Removing "I'm new here" or "Thank you"
Most of the time there is something else wrong in these posts too so editing out just these statements would probably be too minor. But you should improve them and mark the original edit either helpful or unhelpful depending on how much of the original post they edited.
What about when some user is flooding edit queue with formatting changes like the ones I've mentioned above?
If they are flooding the suggestion queue leave them a custom rejection message. They may or may not read these but its the best you can do (other than flagging a moderator). Also if too many of there edits get rejected they will be banned from making suggested edits for 7 days.
Overall think about this when you are approving or rejecting as too minor. Should this post be bumped to the front page because of the edits this person made? If the edits are insubstantial you should be rejecting it.