Swedish here. There are deductions you can make but for the majority, it is either simple, or it has been prefilled. For example, for retirement savings of a very specific kind (IPS for Swedes reading this) there is a possible deduction and I believe it is pre-filled. Same thing for interest on house loans (I believe).

For capital gains vs losses, when you trade with stock, you however have to do it "manually" (not pre-filled). (For Swedes: K4 I think is mandatory but can easily be computed by your portfolia broker such as Avanza).

I think today the website that the Swedish tax office provides for you to actually fill in and confirm your tax statements is like a free, online version of what previous generations commercial tax software was about. Every year it includes yet another bit of functionality that simplifies it or handles a new corner case. For the majority it has been very simple for quite some years - send an SMS to confirm the pre-printed statement for example. But if you trade with shares, or if you have a business, or for example own forest (which automatically makes you a business), it is not as simple yet.