What will be the impact of Brexit if I wish to go to the UK for a short stay, without seeking residence there?
EU citizens can continue to travel to the United Kingdom starting from or after 1 January 2021 for vacation or short stays of maximum 6 months without having to apply for a visa. The British Home Office made an announcement about that. Please note that this does not, in principle, apply to visits for work or study in the United Kingdom, for which a visa is required. The British Home Office also made an announcement about that. Presently Belgian citizens can still travel to the UK with either a valid identity card or a valid passport. From 1 October 2021, the British government will only accept a valid passport for short stays in the UK.
Please take into account the since 1 January 2021 revised travel advice for travel between the EU and the United Kingdom (link).
Individuals already legally residing in the United Kingdom before or on 31 December 2021 the latest will be able to travel in and out of the country when in possession of a valid identity card or passport. For non-EU family members, a valid passport is required. See question 1 and question 2. With a “pre-settled status” or “settled status” you will have the right to enter and leave the United Kingdom provided you are in possession of a valid identity card or passport until 31 December 2025.