Hello,
I was wondering if it's possible to render, for examples: 'Character' and 'Background' layer animation separately.
So I get 2 PNG sequence, 'Character' and 'Background in the end.

If it can be cropped to match its frame size per layer, would be super cool.

Is this possible?
Thank you!

If you turn off the 'Character' layer, with the eye/visibility icon which is on the Layers docker and the Timeline docker, you can render out just the 'Background' animation. Then do the same process but with the 'Background' layer turned off.

The rendered output images will be at the frame size of the image so I don't know what you mean by "cropped to match its frame size per layer". Can you explain that more, perhaps with a full screenshot?

I see, that work nicely.
About the cropped one, I ended up with 'Trim to Layer' for each layer to render.

Probably oot, but is there any 'Export scale' or 'Output scale'?
Right now there's one for video render, but it makes the image blurry if I change the Height and Width up.
Or I will just resize the entire image before exporting for now.

Thank you!

Trim To Current Layer is useful for cropping to drawn crop marks (or whatever content is there) and can be used to extend the canvas in the same way.
Trim To Image Size is useful for getting rid of any off-canvas content that you may have created, either accidentally or deliberately.

I've never used the Render width/height to change the image size. Depending on what resize method it uses, you may get a better looking result with Image -> Scale To New Image Size before you render out. The Bicubic filter seems to be the best general purpose option but you can try the others to see what they do.

The manual will probably give an explanation. It's well written and presented with good search capabilities: https://docs.krita.org/en/