The 5G frequency band used by your provider in your country is the most important thing. Since you’re in Italy it’s probably n78.
My guess is you’ll be fine with both phones all across the EU, but there has been some confusion about the FP5’s support of this wireless band, since the Qualcomm hardware it uses does support the n78 frequency band, but it’s not explicitly listed in the FP5’s specification - but that’s most probably an editorial oversight, since most of Fairphone’s customers are in countries where this frequency band is very widely used for 5G.
I suggest you google something like ‘5g wireless band [provider name]’ or ‘5g frequency band [provider name] Italy’ and compare the result against the phone’s technical specification. But as I said - I wouldn’t worry to much about support in Italy.
Edit:
Wikipedia lists n28 for the provider ‘Iliad’ in Italy:
That one is listed as supported on both the FP4 as well as the FP5 according to the linked sources.