My wife volunteers during tax seasons to do tax returns for low income people. It always depresses her when people on the lower runs of the ladder come in and have been doing uber, lyft, doordash, etc or some combination and have nothing more than a hand wave estimate of how many miles they drove. She is the one who has to tell them just guesstimating is not allowed and what might have been a $1000 check back to them is instead a $2000 check they need to write to the government. 9 times out of ten they say, "but I don't have that money" and it crushes her. More than a few get mad at her for not being willing to just enter their guesstimate into the form.

I'm not sure if it is because uber (or whomever they work for) didn't make it clear enough to track it properly or if they simply didn't take it seriously.

You don’t need an LLC to do this. Just filing a Schedule C will do.