How to prevent papers from being published in advance by others? I have a new idea, and the experimental results are also good. But my mentor does not allow me to publish it yet. But I am worried that the idea will be robbed by others. So is there any way to not publish it now, but I will take advantage of this idea first？
I am a computer major, and I mainly publish conference papers. If I upload the paper to arxiv, will others not be able to use the same idea as me?
If I upload it to arxiv, many people will have seen this paper. When I submit this paper again after a year, will it be because it is a previous one, and everyone has seen it, so it won’t be accepted.
If I upload the paper to arxiv, will others not be able to use the same idea as me?

They absolutely can, but because you have uploaded your paper, you have established precedence: you can claim you had the idea and did the work first. Others can still use your idea (and you should feel flattered they do!) but they would have to cite you.
There are many papers on the arXiv that have accumulated lots of citations but have never been published in journals, e.g. this one. If the authors of that paper ever submit it to a journal, there's a high chance it will be published quickly, simply because it is so impactful.