Estate tax return and escrow on closing – Foreign decedent on title

My father and I are selling our Florida condo with a closing date in May. We are Canadian citizens and we owned the property with my mother who died in 2021 (joint tenants with right of survivorship). We did not know that we had to file her estate tax return so we have an accountant working on that now. We understand that this could take over 3 years to be processed.

We are confused about how much of the sale price must (?) be withheld in escrow at the time of closing, until the IRS lien can be removed from the title. The accountant has both said that the IRS decides the amount, or that the title company ultimately decides how much to withhold, based on the title company's risk assessment. The accountant said that the title company should withhold 100% of the sale price, because the IRS requires this (?), but that the title company may decide to release "some funds".

With the U.S.-Canada tax treaty, I presume that we will have zero estate tax owing. As such, I do not see much risk for the title company that would necessitate a 100% holdback. Needless to say, we do not want all of the funds held up for 3+ years if we can avoid it. Any thoughts would be greatly appreciated.

I am also wondering about the 4422 process with a U.S. executor – online searches suggest that this could speed up the removal of lien (and release of funds?) significantly, but I have no idea if this is true.