You are watering it way too much. Monsteras need to need be soaked then allowed to completely dry out between waterings.

A larger pot allows for less frequent waterings. I only water mine monthly in the summer. Every 2-3 months in the winter.

They need fertilizer especially when putting out leaves. Yours is showing nitrogen deficiency. It's a bit of a weird expression but monsteras are unique.

Light levels - they do best with 3-4 hours of direct sunlight every day. Generally it's best to have those hours in the morning or evening.

Repot it.

I know others have already said you're watering too much, which is probably true, but I noticed this looks like a thai constellation. I think it might be getting sunburnt based on a similar thing happening to mine 2 years ago. Are the brown patches happening in the completely white parts of the leaves? If so that is probably it rather than too much water.

If you can post a picture of the soil by lifting it out of the nursery pot that would be helpful. That way people can see the root condition and type of soil that it is in. The suggestions for repotting it might be needed, but not the priority action if the browning isn't caused by a soil/water issue.

If you move the plant to get less sun and repot it all at the same time it could be a big shock to the already struggling plant.

It might be that you should move the plant then a month later change the soil, but without seeing the soil it is hard to be sure.

In general it sounds like you are watering too much, but those problems might not have materialised yet if you only had it 6 months. If possible, invest in a moisture probe and only water when the soil has dried rather than on any kind of schedule.

How much water are you giving it with each watering? It looks like overwatering, but it can be saved if you let the soil dry out and reduce how often you water it.

If you have bamboo or wooden skewers, stick one all the way to the bottom (gently, and closer to the side of the pot where you won't snag the roots). Pull it out after 5 minutes. The skewer shouldn't be bone dry at the end, but it shouldn't be too wet... It's hard to explain but you'll eventually get a feel for what seems right.

What I'd much rather know, where do you get information how to care for all kinds of plants without having to ask in Lemmy communities or whatever? There must surely be some place where someone collected all kinds of plant growing information like this, right?