I see. It might help you to know that as long as your game is free to download (you do not charge anyone for your game) you can easily use royalty-free backgrounds and character resources from itch.io and others. When you say "commercial game", in most western platforms it means that you will be selling your game for money. If it is a free game, "non-commercial", I believe many resource creators here will probably say you can use their resources freely. In general, I feel many of us on itch.io are very relaxed as long as there is no money involved, so you should have no problem as long as you ask permission, credit properly and do not ask people to buy your game.
It's nice that you're studying, researching sites, asking politely and linking back. I feel your courtesy will make many of the itch.io resource creators happy.
Ah.... about making more free assets... In all honesty, I don't get a lot of comments/ratings for my games and resources, even though they're free, so I've slowed down on making them and spent more time doing other things instead. I've spoken to one or two developers on a Discord server, I found out that they too have stopped making so many free games because nobody is giving them feedback. It may be why there are fewer free games and resources overall nowadays. It's a bit lonely, so a number of us give up after a while. _(:з」∠)_
If it helps, there are quite a few assets that are only $1 or even $0.50 which you can buy. They're cheap, and the best part is that once you buy them, you can usually use them in any commercial and non-commercial game.
Happy Chinese New Year to you too~