The simple answer is: Yes, but.
Data allowance is generally unlimited, but the amount of high-speed data you receive depends on your provider and plan. You usually get 1–3 GB of high-speed data per day; after that, speeds drop to 1 Mbps or less. 1 Mbps is enough for WhatsApp and casual browsing, and maybe even for music streaming, but nothing more. You can’t watch movies at that speed anymore, and even photos take a long time to load.
Why is that?
International providers purchase data plans from local network operators and often use them while roaming. As a result, they usually have to pay these network operators’ roaming rates—offering unlimited high-speed data would very quickly drive them into bankruptcy.
If you compare the cost of fixed data plans across different providers, it becomes clear: it doesn't make sense that you should pay less for unlimited data than for a fixed data plan.
Example: Airalo:
3 days of unlimited data for €8.50
10 GB of fixed data allowance for €10.
Unlimited plans include 3 GB of high-speed data per day.
But my provider says it offers unlimited data
See above—yes, but.
The problem is that some providers, such as Airalo or Roamic clearly communicate what you’re getting. Those are the positive examples. But there are also negative examples, such as Holafly, where you have to explicitly ask which plan offers how much high-speed data per day, or providers that don’t disclose this information at all, like Telefonica’s Travel eSIM division. Therefore: if details are missing, it’s better not to buy, because the surprise could otherwise be a negative one.