I'd say report all of your cryptocurrency gains and losses when you file your yearly self assessment that way you've covered everything.
If you're going for a shared accounting pool system I found that's the easiest. If you're going for the bread and breakfast rule or the same day rule then taxes are worked out differently. Did you speak to any accountants about what's the best option for you?
You've made mistakes in your example. If you're starting trading cryptocurrency in January 2021 then any income you've made from the first trade until 5th April 2021 is something you've got to make a note of and declare to HMRC whether it shows profits or losses.
Remember for year end April 2021 (which is April 6th 2020-April 5th 2021) you've got to file your self assessment by January 31st 2022.
So this means, no matter what value my gains are (under capital gains), I will still need to report it?