A DJI Mini2 falls under the category of ‘open’ and subcategory A1
For Belgium:
There is not specific training required for drones lighter than 250gr, but it is recommended to take the free online course offered by the Belgian CAA for A1/A3 flights (link)
You can find more info on: https://mobilit.belgium.be/nl/luchtvaart/drones/nieuwe_regelgeving/categorie_open
For the UK:
For drones with a camera, lighter than 250gr you are only required to get a operator ID. A flyer ID and corresponding training is not required.
More info on: https://register-drones.caa.co.uk/drone-code/getting-what-you-need-to-fly
For the Netherlands:
Also in the Netherlands there is no requirement for a training for drones lighter than 250gr. You do need to register at the RDW as a drone operator.
https://www.rijksoverheid.nl/onderwerpen/drone/vraag-en-antwoord/regels-drone-laag-risico
For Luxembourg:
Also in Luxembourg there is no requirement for a training for drones lighter than 250gr. You do need to register as a drone operator.
https://dac.gouvernement.lu/fr/drones/where-when-register.html