It depends. Unless you use the accrual method of accounting, income that was received from a grant for producing a performance that was postponed due to COVID 19 cannot be postponed. This is because the income was constructively received in 2020. Constructive receipt means that you had the right to receive it and it was available to you, regardless of whether you cashed the check or not, so to speak. One example of constructively received income is prepaid income.
Here is a page on the IRS website that explains constructive receipt of income