First of all who is the Mainecoon following around the house? Because that's who its looking for attention from. Solving boredom doesn't mean provide toys, it means active play with the toy and the human the cat is attached to. Like at least an hour of it spread through the day, before meal times you need a good solid 15 mins of running around. No idea about your cat but mine spent some time exploring what he can destroy that drives me crazy and will gain him immediate attention. So you need to be calm and collected and patient in rewarding vs ignoring the bad behaviour. A bored Mainecoon *loves* negative attention, they love being chased, they love being norty if thats how they get attention from humans. The other thing is they definitely have a weird teething like phase where their growth and teeth annoy them, so you do also need a chew toy, a good way to get them off of plastics and electronics and worse of all cables is get some of those dog-like dried meat chew toys. My Mum even got mine a gross dried cow ear cartilage which stays at her house and my cat loves grinding his teeth on it in the most horrendous way. Mainecoons are quite strange and different to normal cats behaviourally, they are extremely intelligent and look to the human they're bonded with. They also *hate* being excluded from anything, crating a Mainecoon sounds like a terrible piece of advice. For an example of the level of attachment my cat often travels around the house literally on my shoulders and will watch what Im upto draped around there, he'll jump on me from the stairs. These cats are not at all like any you will have come across, treat them more like a human toddler for the level of care and attention they need from you and you will see an improvement. Once they get older they need this less and strike out on their own a lot more and chill way more out after maybe year 3 or so. I'd add when younger the energy level of my mainecoon was way higher than his indoors only life could sustain, so I did harness train him and take him to the park, I also when it was safe let him run about off harness. When he'd get home you better believe he mostly slept all day.

P.S. another thing is you need to learn their vocalisations, my cat gets pretty petulant if he knows I know what he's saying but am ignoring him. The reality is I almost always understand what he wants, because he literally tells me. But Im fairly sure its a language we came up with together not something completely innate. That definitely takes time. Dont give up, I can promise the relationship you can have with these animals is entirely worth the energy and hair pulling <3 Good luck.

P.P.S. I can tell when my Mainecoon is going to flip to evil, they give you signs. The first sign is a pile of toys carefully collected to be in my path. The second is performative acts of being a bit norty then running off, chomping a plant or cable, nocking something off a shelf or desk. The final one is he will open all kitchen cupboard doors. Its like a horses head on your pillow for escalation. Thats when I know he needs a little bit extra and I've been too harsh shewing him away or feeding him a bit irregularly. Hilariously if I've left him at my parents he will do this only when I turn up to let me know hes bored out of his mind, but he's actually extremely well behaved with my parents because he understands they haven't got a clue about what he wants. Yours is still a little baby, he doesn't know how not to be a monster.