Do colleges see senior year ECs?

As the title says, I was wondering to what extent do colleges see senior year extracurriculars, if at all? I know they look at your senior year schedule and sometimes your first trimester/semester grades but do ECs matter during senior year if they happen past the application deadline? I assume senior year student council would still be valid on your college application since the results for student council would be announced towards the end of junior year, but what about ECs taken after the college application deadlines? The reason I’m asking is because I’m pretty much guaranteed to be the or one of the varsity tennis team captain(s) senior year, but since tennis is a spring sport I don’t know if colleges will see it. Should I try to be one of the team captains junior year so I know that colleges will see it for sure?

Extracurricular activities aren’t on your high school transcript, so colleges will know about them only if you include them on your application (or if you email them with an update after you submit your application).

if it’s a spring sport it may not happen before decisions are made, but regardless you can let the schools know by sending them an update