Unfortunately, all EU rules on freedom of movement ended on Dec. 31, 2020, for EEA citizens. You will not need a visa to visit the UK. You can stay in the UK as a tourist for up to 6 months without a visa. You can visit the UK on holiday or to spend time with family and friends. But while in the UK as a tourist, you cannot do paid or unpaid work for a UK company or as a self-employed person; claim public funds. (See: https://www.gov.uk/government/publications/public-funds) You can live in the UK for long periods of time through frequent or successive visits. But to marry or register a civil partnership, or give notice of marriage or civil partnership. You’ll need a Marriage Visitor visa. (see: https://www.gov.uk/marriage-visa) If you would like to stay beyond the standard duration, you will need to apply for a visa via the following website: (https://www.gov.uk/check-uk-visa)
If you are in the UK now, then you must apply for the pre-settled status. It is a very straightforward procedure in which you log into the government's settled status website.