Wow. That's a real monster! Good for you. You must be doing everything right! Moss pole or some other support system. You can build a teepee structure with three bamboo poles and some wire at the top. There are also square tomato cage-type supports that you could use.

You could also trim some off and propagate it to make more.

its probably time to propagate some fresh new pieces.. and once you get those going.. just get rid of the old plant ..

since the pieces WILL BE the old plant .. all you have done is turn grandma into granddaughter ...

https://duckduckgo.com/?q=Monstera+propagation&t=ffcm&iax=videos&ia=videos

great time to do it ... as you can have a well rooted.. newly potted vigorous plant by fall ..

i found.. the problem with old huge plants like this.. is you probably need to repot.. and thats isnt easy with a monster ... and it will be hard to make it sit still while the roots take hold ... etc ... just a big mess ..

and if you make extras.. you can give them away as gifts ...

ken

In my brief (3rd year now) experience with monstera, you can just ruthlessly chop it until it is small and cute again. Since it's obviously happy and putting out new growth, it should keep going.

I'm not sure how long one can keep doing this before you need root pruning, but it seems to be a such a vigorous plant that you are probably free to make some mistakes.