My answer in the tread referenced above provides some similar information but does not directly address all of the specifics of your situation.
I assume that the bank in question is the custodian of this IRA. A lump-sum distribution to the estate is only required if the bank's IRA agreement signed by your aunt requires it. Otherwise, the tax code does not require a lump-sum distribution to the estate. Instead, the funds can be trustee-to-trustee transferred to an inherited IRA with the estate as beneficiary. At the direction of the executor or personal representative of the estate this inherited IRA can then be split into separate inherited IRAs, one for each of the estate beneficiaries and distributed out of the estate intact to each of the estate beneficiaries, allowing the estate to be closed. Otherwise, if the inherited IRA is retained in the estate the estate would have to remain open as long as the IRA still contained funds that were being distributed to the estate. Whether or not this split is done, because your aunt died before her required beginning date for RMDs and the beneficiary was the estate (not an individual), the 5-year rule applies, requiring only that the inherited IRAs be fully distributed by the end of the fifth year after the year of death. (It seems that she died in late 2019, so that would mean that the inherited IRA(s) must be fully distributed by the end of 2024.)
Any amounts distributed to the estate would generally be passed through on Schedules K-1 to the estate beneficiaries to be taxed that the beneficiaries' tax rate; the estate would then take a deduction for this Distributable Net Income so it would not be taxed at estate tax rates.
Depending on the amount involved and the particular desires of each of the beneficiaries, with a separate inherited IRA established for each estate beneficiary, each estate beneficiary could separately decide how much to distribute each year between now and 2024.
