Good news! Roughly 1% of US people surveyed in 2025 voluntarily identified themselves as transgender, and since a great many in the US would be too scared to reveal this info about themselves, the number may be substantially higher. But let's work with 1%.
So it would seem like cisgender folk are at least ~10x as likely as trans folk to do mass shootings :)
Do I think that being cisgender predisposes you to mass shootings? No, obviously. But the narrative being imposed in media is that being transgender does do so.