Do I need to declare crypto earned through mining?
If you are mining as an individual then the proceeds are classified as income from a hobby. Hence, you are required to declare and pay Income Tax on mining proceeds. This is the case regardless of if you convert the proceeds to fiat (SEK). The value you need to declare as income is the value of the mined coins on the day that you mined them.
If you're mining as a hobbyist and made a profit you need to declare this in your T2 form. If you sell any of the proceeds at a later date you will have to pay tax over your capital gains which is declared in your K4.
You should set the cost basis of the newly minted coins as equal to the amount you declared in income. Which is the value of the proceeds in local currency on the day you mined them. You can read more about how mining is taxed in our Swedish tax guide and in our guide on declaring mining income in Sweden.