Is show choir a good extracurricular to do in highschool? Will it help with college admissions?
There is no such thing as a globally "good extracurricular" which will help you get into college. If you engage in an extracurricular for the sole purpose of having it help you get into college, it will not help you get into college.
The purpose of ECs are to engage in stuff which is not included in your high school curriculum. Colleges look at extracurriculars to learn stuff about you which they cannot learn from your GPA or test scores. They mostly want to know whether you are a person who is willing to invest time and effort in things about which they feel passionate, what talents and skills you posses, and what are your interests and passions.
Extracurricular activities are for you - to help you develop as a person, to allow you to engage in your passions and interests, or to discover new ones, or to showcase your skills and talents. Those are the considerations which should go into choosing your ECs, not some silly game of “guess which activities college admissions will like in another four years”.
Do you want to engage in show choir because it is something which interests you? Then do it, and stop worrying about anything else.
Okay, thank you for the reply. I am passionate about show choir and will go for it. Thanks again!
For colleges, what matters is how well you do in the activities you chose. So, if you live show choir, go for it! 
@J4eJ4e My S19 was a 4 year show choir kid. I think show choir is just as good of an activity/EC as any team sport. His choir was award winning around the country and he took a leadership role on and off stage. Many of his essays centered around his time and some of the trials and tribulation he encountered in show choir. If you enjoy doing it, don’t hesitate in participating.
It’s hard to answer your question “Is show choir a good extracurricular to do in highschool” without knowing what schools you are targeting. ECs are not important at many/most colleges; any participation is enough. At very selective colleges they want to see achievement/leadership so just being member of a team/choir is not a strong EC. You can look up what colleges you are considering say about the importance of ECs jn admission in their Common Data Set report.
But I’m going to answer the question you didn’t ask, “should you do it?” To that I’d give an enthusiastic yes! It’s something you say you really enjoy, and that’s enough.
Now if you’re thinking of very selective schools you might want to think also of activities that show achievement/leadership, perhaps even figuring out a way to do this with your interest in choir (eg. take a leadership role in arranging performances in your community such as at a senior center, fundraising for trips your choir can make, arranging for someone of note to hold a workshop at your HS, etc; the only limit is your imagination)