I like playing games, not online games, but single-player games such as RPGs with a cinematic story.

"RPGs" should be plural unless there's only one RPG you like to play. But since you said "games", I assume not.

I also like oil paintings.

"oil painting" on its own refers to the activity, oil paintings refers to the objects, and might mean that you like e.g. going to galleries to view paintings, rather than the act of painting.

I think I should more go outside more, though.

I like playing games, not online team/multi-player games, but single-player games such as RPGs with a cinematic storyies.

When talking about things you like in general, it's usually plural (I like a cinematic story means just one, while cinematic stories means what you like in general)

I also like doing/making oil paintings.

It's better to be specific about the action of 'making a painting - if you just like oil paintings, it means you only like to look at them

I can forget about aneverything and only focus on the art while painting.

I think I should more go outside more, though.

I like playing games, not online games, but single-player games such as RPGs with a cinematic storyies.

- If you are talking about things in general, it's always plural. If you want to talk about a specific RPG you could say 'such as an RPG with a cinematic story'

I canget to forget about aneverything and only focus on the art while painting.

- 'get to' is a better verb here I think as it puts emphasis on the painting being the activity that allows you to forget about everything as opposed to just you allowing yourself to forget about everything whilst you happen to be painting