Zorc is saying "definitely closed".
Close of 2019 summer transfer window - August 8
Close of 2018 summer transfer window - August 9
Original date for close of 2020 summer transfer window - September 1
When Sancho extended his contract with Dortmund for a year, he probably inserted a clause saying that if Dortmund got their expected fee (at that time, pre-COVID, 120m euros would have been what Sancho, before his 20/20 season would have commanded) he could decide where and when he wanted to go. This gave Sancho huge power in deciding where he wanted to go as well as the possibility of getting a signing-on bonus like a free-agent would have gotten.
In return, Dortmund probably said that they should be able to get this deal done by August 10 of the summer window, a time that would give them about 3 weeks extra to get in a replacement.
United probably indicated to Dortmund that they were ok with this structure but then COVID happened and players like Leroy Sane were being sold for 45m. They then thought that this Act of God invalidated previous agreements and pushed for a cheaper fee.
Understandably, Dortmund balked at this changing of terms and said 120m by Aug 10 or nothing. United have not paid that yet because they are relying on Sancho to kick up a fuss, the only way out of Dortmund that has worked (Aubameyang, Dembele). The problem is that Sancho has not done so visibly enough for long enough and now Dortmund has the option of weathering his strop and pacifying him with more wages and waiting for next summer (when others will be able to bid) and spending another season with their undeniably exciting team this year.
The question here is how badly did United want Sancho. For example, were he a generational talent like Greenwood, it would make sense for United to just have paid the 120m by Aug 10 and relied on appreciation and football performance to compensate for the extra 30m (estimated) gap in their valuations. But, if he were a Mkhitaryan/Kagawa type player, then United would be correct in not being raked over the coals in an unprecedentedly uncertain economic climate.
Dortmund has a cost to letting him go this late because any replacement would be more expensive. However, there is a benefit to letting him go for a face-saving fee (100m is a round number) because if all the big young talents watching this saga now demand a low buyout clause from Dortmund a la Haaland before they join, their business model is dead.
As for United, I would say that Sancho is generational and any gap in valuation paid now pales compared with the 500k/week he will expect to make in a few years if the transfer works as expected.