I think you should check with Thunkable Staff. While I don’t see anything about it in the Community Guidelines, I can tell you as a moderator for another game developer community a few years back, we did not allow it.
Can you delete some unneeded projects from your current account? Can you upgrade to Pro which gives you more space? I don’t know your age but… maybe ask parents to help with affording it or do some work for your family/community to earn enough. Pro membership is great… you can publish to the web which makes testing really fast and allows you to share your projects with the world much easier.