After you file

sorry for your loss.    Normally, a taxpayer will qualify for the full amount if they have an adjusted gross income of up to $75,000 for singles and married persons filing a separate return, up to $112,500 for heads of household, and up to $150,000 for married couples filing joint returns and surviving spouses. Payment amounts are reduced for filers with incomes above those levels.  so if the AGI test was met for the month he was alive in 2021 he would have been qualified for the payment and you as his heir would be entitled to cash the check.