According to an Italian bassoonist I know, Fixed Do is preferred in Europe, or was at the time he told me that about 15 years ago.

I think I have a different understanding of moveable Do. I was taught (in the US college system in the 70’s/80’s) that Do is always the tonic of the key, which makes it quite confusing after a certain time period since modern music often did not center around a key as much and/or determining the key and key changes can be more difficult. Also, in the Romantic period, keys began to change more frequently and transiently than in previous eras, so what do you do there? Needless to say, I struggled a lot in my ear training classes because of this. When I found out that fixed Do was more common in Europe, I immediately changed and I do change the syllables for sharps and flats with it which I prefer much much more. Maybe I am not understand something about your description of moveable Do or things are just described differently in different countries.