I am sorry for your loss.
Recovery rebate credits may be claimed for individuals who died in 2020 or 2021 when filing the decedent’s 2020 tax return. This includes someone who filed joint tax returns with a spouse who died in 2020 or 2021.
As stated by the previous responder, be sure you use married filing jointly filing status for your 2020 tax return. If you do not remarry in 2021 or later your new filing status will be single, unless there are any qualified dependents involved.