It is an auction and everyone pays the same price. During the afternoon tomorrow every household in Finland will be paid significantly for their power usage unless they have a fixed price agreement, which is not that common

According to Finnish Energy Authority (energiavirasto.fi), at the end of 2022 only 13,7% of customers had a contract where pricing is tied to the hourly market rate. It is much more common to have either a fixed price contract (usually for a term of 12 or 24 months) or a contract where the pricing is set by for example monthly averages of the market price.

My mistake! Assumed all Nordic countries were the same

I'd suspect that actually fixed-price agreements are very common, and represent the overwhelming majority of contracts for residents/individuals.

I know that after the war started spot-prices rose sharply and a lot of people made the jump. Some, unfortunately, locking themselves into relatively expensive prices.