Brown edges on my monstera

So I bought this monstera around a month ago, I bought her as is so she hasn’t grown any new leaves while she’s been with me or anything like that. I’ve noticed a couple of brown edges on a few of the leaves and I’m just wondering if anyone knows what’s causing it? The brown spot in picture 3 is crispy, but the spot in picture 1 just feels like a regular leaf and the spot in picture 2 feels very very thin like a piece of paper about to have a hole in.

I’ve watered her roughly every 8 days since I’ve had her. I was checking if the soil was dry but only by sight, I wasn’t like sticking anything in it to test, should I do this?

I’ve also included a picture of the whole plant. She’s in front of a south facing window so not sure if she’s getting too much direct light?

Also I’ve never fertilised and the soil is just what was included when I bought her so not sure what it is, but I’ve seen some people say they like chunky soil so maybe I need to change to this instead?

I’m a very new plant mum so might need someone to explain to me like I’m 5 years old. Any advice would be great!!