As a non European, prepaid sims in Europe are complicated. Some companies won’t sell sims to foreigners, some have little to no roaming. Some have activation fees that double the price.
Some examples: in Germany you need to do a video call to activate your sim, in Italy most providers require you to have an Italian tax number to buy a sim. In Romanian most of the plans have a paltry 1 GB of roaming.
Also most of the SIMs geared toward tourists don’t allow roaming.