How many Grant Rounds can I enter?

You may submit a grant for as many rounds as you like. It is possible to be accepted into the Main Round and multiple side rounds up to a maximum of 5 rounds in total. There are some rare situations in which this norm doesn't apply.
The Gitcoin team will review each submission per platform and main round to confirm eligibility. However, round owners review their applicants separately based on their own rules and some feedback from FDD, and the Gitcoin DAO.
In a protocol future, round owners will be able to configure their rounds independently. Check out this article to prepare for your Grant Round: