DJI Mini 2 style drone allowed in Europe

There are many rules and regulations to be aware of, but the good thing is that they are (as far as I know) the same in the entire EEA.

A big question is how heavy the drone is.

The drone exactly is DJI Mini 2 which is 249 grams in weight.

https://www.gov.uk/government/news/drones-are-you-flying-yours-safely-and-legally

https://www.easa.europa.eu/en/the-agency/faqs/regulations-uas-drone-explained

Hopefully the above get you started

Drones in EU (plus Norway, Liechtenstein, Switzerland and Iceland) are regulated by the EASA (European Union Aviation Safety Agency).
https://www.easa.europa.eu/en/domains/civil-drones-rpas/open-category-civil-drones
UK has it's own rules and requires different registrations (refer to the link shared by Joe).

In EASA countries as a non-EU resident visitor you would need to register as a drone operator with the National Aviation Authority of the first EASA country you intend to operate from. It’s then valid for all other EASA countries.
In order to avoid any language issues I think your “intended first country” should be Ireland.
You need to read through the rules an pass an multi-choice online exam.
https://www.uaai.ie/drone-laws-ireland

In addition to EU wide rule there may be additional country specific requirements like a compulsory liability insurance that includes drones. Some countries like Croatia, don't allow to take fotos and videos without special permit.
I use following web site (German only) to get an quick overview about country specific rules
https://drohnen-camp.de/reisen-mit-drohne/

That's great, if the drone weighs less than 250 g you don't need a licence to fly it. But you still need to register as a drone operator and your drone needs to be clearly marked with your operator ID-number.

In addition there are a number of rules and regulation about how you can fly. E.g. maximum altitude is 120 m above ground level, you may not fly above crowds and you must always be able to see the drone. And always check with the relevant government agencies for areas where drones are banned.

And some countries have additional regulations. Croatia was mentioned, but Sweden also has very strict laws on aerial photography.

Good advice provided already.

I use FlyNex map to look where flying drones is allowed.

And signs on government fences showing a picture of a drone with a bar through it.

Having every country in one map is useful, but always check with the local authorities. I did check the map linked above and it's not entirely correct for Sweden.