It depends on when studios are actively inviting potential show creators which usually happens when they host a shorts programme, but even then they gets tons of submissions and a lot of these are internal.
Even in normal times, they get loads of project proposals, they're still accepting pilot ideas, but they still get a lot and if the pitch bible isn't good enough or the premise of the show isn't what they're looking for in the opinion of the execs, they instantly reject it.
I wouldn't take rejection to heart and it doesn't necessarily mean the show idea is good enough, the studio can only make so many shows at one time, even if it makes it to pilot stage.