I don't think I've ever encountered someone claiming that queerness is bourgeois, actually. Is that a common claim?

This actually goes back to the USSR in the 30s, where, after a repeal of Tsarist law in the country led to a ~Decade long sexual revolutio.

But Stalin's rise to power, and subsequent anxieties related to geopolitical isolation and the buildup to WW2, led to a socially reactionary turn, and homosexuality was criminalized.

The reason given by some was that Homosexuality was bourgeoisie decadence.

This is, of course, silly. But that's a line that persists among some ML parties. For example, in the UK, most ML orgs still hold to this line of thinking. While your pro-lgbt socialist orgs lean heavily Trotskyist.

To add to what SpookyBogMonster already said: On an international stage the big proponents of these views nowadays are Xi Jiping's faction in China or North Korea, while even Cuba (which had upheld these views for a long time) have now abandoned this position.

In the US and in Europe, it's a fringe position among leftists, mostly popular with those who also hold favourable views of Xi Jiping's China and North Korea. It's a very vocal minority though and infamously one of the key developers of the Lemmy platform is one of those.