The main thing is not to do problems, but to learn some methods to solve mathematical problems. Because if you study for a doctorate, you won't have much free time. It may be more difficult to make up the foundation of mathematics. Therefore, when filling the foundation, the most important thing is to find an efficient method.
If I think my method is inappropriate and wastes too much time, I will change it immediately.
It's just a matter of dabbling. Don't waste too much time on one issue. If you don't, you won't. You should ask others in time, and then you should take it seriously in time when taking online classes, and then you should make a summary in each class.