The United Kingdom left the European Union on 31 January 2020. From 1 January 2021 the relationship between the UK and the EU is governed by a new agreement on trade and co-operation, as well as be a previously reached withdrawal agreement.
As a Swedish citizen living in the UK by end of 2020 you will, if you intend to stay after 2020, have to apply for settled status:
EU Settlement Scheme - you will find all information via this link
If you have not yet applied for the EU Settlement Scheme and your passport has expired, you must call the EU Settlement Resolution Centre and ask for a paper application. You will need to inform them that the reason you cannot apply online is because you will not obtain a valid passport before the application deadline.
More information can be found on the UK Government website here.
The UK has introduced a points-based immigration system that will treat EU and non-EU citizens equally. If you plan to move, work or study in the UK you will have to apply for a visa before you come to the UK. Read more here.