You are not an "eligible designated beneficiary," so you have to use the 10 year rule.
Under the rules created in 2019 as part of the retirement security act (forget the exact name), you must withdraw the the account and spend it out within 10 years.
Additionally, if your mother did not take her 2020 RMD before she died, then you were required to take it and pay the tax (in 2020). If you did not do that in 2020, there may be substantial penalties at this point and you may want to contact a tax advisor to help you.
Then, there is a new proposed rule that owners of beneficiary IRAs under the 10 year rule must also take an RMD each year. I don't think the rule is final, but you probably should take the RMD as if the rule was final, because it could be finalized at any time.
@dmertz ?
