“Homophobic stuff” is pretty broad. If you’re wearing anything related to the Qatari regime, you are representing a homophobic group, but I wouldn’t rate that as an attempt to harass or marginalize anyone.
Aggressive displays of homophobia and wearing a rainbow are not the same thing.
One is an expression of solidarity for a group, the other is an expression of hate against a group.
Wearing a rainbow isn’t hateful, and isn’t intended to threaten anybody. Displays of homophobia usually are.
Comparing the two relies on a false equivalence that is commonly used by homophobes to try to justify their hatred of others.
If the Qataris wanted to show the world how much they treasure heterosexuality in a way that didn’t seek to harm or marginalize other groups, then I don’t know why we would object.
But that’s usually not how homophobes choose to conduct themselves, funnily enough.