I haven't seen a concise list of requirements as to what I need to have in order for me to drive my UK registered car in Europe after Brexit. (after 31st Dec 2020)
I know how strict eg. the german TUV is, compared to what is required for an MOT in the UK - I believe until the UK was still part of the EU, as long as a foreign car had a valid technical / mechanical approval (MOT), it was accepted as safe to drive on any road (with the exception of the ominous stickers on the headlights, not to blind the oncoming traffic - left hand drive vs right hand drive)
Edit: this is about using the car for a one-off recreational return trip - max 1-2 weeks