But in my opinion the best solution is to have people bring their own cups and just reuse them, and unfortunately only a small percent of people do that.

It's also systematically/institutionally discouraged at most places. It was before 2020, and even more so now.

Most places (e.g. many Starbucks) will not let you use a reusable cup when you actually try, even while advertising their "green" policies.

Go ahead and try it, most of the time they'll suggest you pour it into your own reusable cup right after they pour it into a disposable one for you.

There are many other reasons to avoid letting a corpo make your drink.