The first houses were AFAIK squatted in 1970 in the Netherlands and one thing that was important to squat an empty building was to have a table, a chair and a bed with you. By using those items of furniture you were officially claiming to be living in the building.
There is a reference in an old archive regarding squatting of land in the 'Veenkolonien' (peat colonies, in the north of the Netherlands) from the 1920's or before, that also mention the need to have a table, a chair and a bed in a shack made of turf/sod before you can claim an unused patch of land (you needed to be able to build that shack within a day).
So I think it is safe to assume you needed at least a roof + the three items of furniture mentioned, in order to lay a claim.
But yet another person claimed that this was also used way earlier in America and was actually introduced by the Dutch and was later changed into driving a stake into the ground.
Is this true? How far does this go back? Where did this come from? Or are we talking about two different things here - squatting in NL/EU and land claiming in America?
To me it looks like that in Europe there is no land "to claim" for a very long time. There was simply no non-occupied patches anywhere and there was no massive migrations to unoccupied land for around 2000 years at least.
This is not my expertise, but...
Land stakes and land grants were a thing used in America as a way to encourage westward expansion among many other reasons (expansion being a big one iirc). I went to a land grant college (Michigan State) where the land was given as long as it was used for certain purposes (I.e. education). People also did go west, find acreage (I am not sure technically how) and then register and pay any fees to a government official in charge of recording that. You were given a deed of land and that showed ownership as well as that you had documented the ownership with the government. After the civil war, many African Americans took advantage of the "20 acres and a mule" promise that also encouraged westward expansion.
Again, so not my expertise (I went to college to understand who Palestinians were and why they burned our flag so much - I grew up in a small town on the west coast) but I did major in History and this is some snippets of what my poor, abused brain cells remember. Sod houses were also totally a thing (aka peat) and Laura Ingalls Wilder lives in one in a book by her (one of my childhood obsessions was reading Wilder). However I don't think land stakes had anything to do with what was on the actual land (houses, furniture, etc) as many claims lived in tents or worse until actual structures could be built.