That is quite normal in Denmark as well. Part of the reason is that the bank cannot approve of the deal, if you have not sold your old house. So either you sell your house and move into a rented apartment, or you commit to buy a house if you can get your old sold in some specified timeframe. Usually the sellers realtor advice the seller if the house is likely to sell or not at a given price.

You can make your offer contingent on selling your old house (or on an inspection, or anything else you want). Sellers are also free to not accept such offers. Both of my house purchases were from submitting a no financing contingency offer with significant earnest money, and I think that helped me win both bids.

Perhaps different today, but back when I lived in the auld country it was totally different in Scotland (still in the UK, I believe).