I think that there were some back then who were known, or at least heavily suspected. Two that come to mind were Liberace and Peter Lorre.
I think Liberace was an ‘open secret’. No one cared because he was excellent at what he did. He didn’t speak to the press about his orientation...he didn’t need to. Women thought he was cute, men respected his talent, even if they saw something ‘odd’ about him. He didn’t flaunt his gayness as in shoving it in your face to get you to agree with him or accept him.
Find some of his old shows and watch the guy play. He was one of the best on the planet, bar none.
As for Peter Lorre...heck, I didn’t know!
Wikipedia states that Peter Lorre (born Lazlo Lowenstein) was married 3 times and had a daughter. I never heard anything about his being gay.