And as you describe in the EU it's "up to 24 hours". And in the lawless authoritarian regime? That Canadian girl was detained for 11 days and was told to prepare to be held for months: https://www.cbc.ca/news/canada/british-columbia/jasmine-moon...
A friend's family flew into a EU country with a letter, they thought this letter was their visa but it turned out to be a rejection from the EU country's consulate (maybe it was a request for more information for their visa application). They were denied entry, but there was no indefinite detention, they were just told to get on the next plane out of the country and had to wait in the "international area" of the airport until said flight.
There must be a probable cause : https://www.service-public.fr/particuliers/vosdroits/F14837
In the US you need probable cause to get pull over or temporary detain you. In France, you don't need probably cause for temporary detaining you, but if they suspect you of something they can also send you to jail. You can't be sent to jail in the US just on them just suspecting something.
Most EU country police don’t need probable cause to detain you. It does happen to be detained for no reason outside of profiling. For example, in France, you can be sent to jail for up to 24h with no probable cause.