Doing research into Bitcoin mining. I would really appreciate some help

Could somebody help me, please?

I've been doing research into how Bitcoin mining works.

I know that there are certain things that make mining harder and more expensive with the time. Could you please explain it in a simple not too technical way?

Are there any events in 2021 that will make it harder or more expensive for miners to mine Bitcoin? Could there be such a big inflow of competition that the mining expense rises drastically from today? Or it's not how it works?

Thanks a lot for your help!