As somebody who has actually dealt with very poor mental health (and who still isn't great) I have a lot of empathy with everyone who is struggling right now, from all walks of life.
However, this whole 'let's use poor mental health' as an excuse whenever the going gets a little bit tough is starting to wear thin. Life isn't stress free, and life isn't fair. I think a lot of people really need to work on their resilience issues when it comes to things like this.
Cancelling exams won't help you. Yeah you might not have 'mental health' struggles if you don't want to sit your exams, but you will end up being stressed out when you get to university (or whatever you plan to do next) and haven't got a clue what you are doing because you didn't have to do any actual work to get there. Look at the mess that happened this year, there are thousands of students across the country who got onto courses they probably wouldn't have in normal times, will probably struggle, and eventually drop out. Do you think this is good for their mental health or stress levels?
No I'm not going to be one of those people who says going to school is useless and we can all teach ourselves. There's a lot more to school (and university) than just the education aspect. Nonetheless, it's your life and your future. If you feel you're not getting the teaching you need, show some motivation and start self-teaching yourself. Motivating yourself and not expecting spoon-feeding is another life skill people seem to lack.