2 - If you chose multiple jobs and were bored in all of them, the problem start to look like it's in you, not in the jobs. Therefore, it's a problem you will bring into your next job, and few companies want that.
When explain that I left my job at a bank after 3.5yrs to go back into videogames dev, nobody bats an eyelid if I say I was bored. Even so, I do not say it, because the important bit is where I wanted to go to, not where I wanted to get out of.
If the company asks you what you look for in a job, frame it in a positive way.. like "intellectually rewarding" without going into the negative part i.e. "I hate getting bored/working on boring projects".
I personally have a decade on my resume where I changed jobs quite frequently. Most of them were contract or consulting work so by the very nature of them, they were short term. Some people take issue with that, others note the fact that I had no downtime between contracts and choose to ignore the frequent changes.
I don't mind junior candidates who change jobs a few times early in their careers as I see that as them getting their bearings, but once people figured out what they want to do, I expect job tenures to lengthen or at least expect people to have a good explanation as to why they kept moving on.
You prefer to do short term consulting work over long term jobs? Fine with me. You joined a bunch of startups that ran out of money after a year? OK.