This section states: "If you have an uncommitted transaction that exceeds 5% of the WiredTiger cache size, the transaction will abort and return a write conflict error".

As part of an unrelated investigation (SERVER-64982), we've discovered that the statement is not accurate, and the by-design behaviour is more generic: an uncommitted transaction can abort and return a write conflict error if WiredTiger is under unsustainable cache pressure.

(There's probably a more rigorous definition of "unsustainable cache pressure". It's likely 20% or more of the cache content marked as dirty. However, this level of detail may be beyond what's expected in the manual, and we'd need input from the WT team if we decided to include more colour around it.)