“””How do we know R vs. D election day voting? Do they get different colored ballots of something?”””
When a person registers to vote, they indicate whether they are Republican, Democrat, No Party Affiliation, or a number of miscellaneous minor party.
When they get a ballot to vote the County Supervisor of Elections knows whether the person was a Republican, Democrat, No Party Affiliation, or a number of miscellaneous minor party.
We do not know how a person voted. We only know the party affiliation of the person.
And since Trump has 95% support among Republicans, we can count on the votes. Thanks for your explanation.