That might be true, in a literal sense. Because permitted flags are generally one of the many domestic national or county ones, sports, clubs’ and the like.
But I doubt that any council has ever sent enforcement officers round to houses telling them to take down Ukrainian or Indian or Polish etc etc flags. I can see that some flags might create a public order issue - like flying the flag of Pakistan in an Indian neighbourhood - but that’s not really about flag flying, but about any provocative message.
There used to be a Brazilian flag hanging from a window in a road near me. It was kept lovely and clean and bright. I liked it.