Have you changed the APN in your phone to “mob.asm.net” for starters ?
As you are roaming on a foreign network, you are reliant on that network’s infrastructure.
Some networks do reserve 5G access for their own paying customers, leaving roamers to use 3G and 4G
Your location will of course play a part, just as it does in the UK - you will get better coverage / speeds in large towns and cities as opposed to rural areas.
You can try manually selecting a network on your phone, rather than letting your phone automatically select a network, as you may then be able to connect to a network with better coverage / speeds.
Also, are you in the EU, where Smarty includes roaming, or outside the EU, where you would need to buy an add on ?
