According to the article Your Copy of the Quran Was Probably Written by this Man (undated),
A Mushaf usually requires more than 3 years to write a Quran and an additional year to proofread it. This means that a single written hand copy of Quran requires a year to be completed.
(Since three plus one equals four, it probably takes four years to create a hand-written copy of the Quran, but that arithmetic issue is not that important here.)
The article Did You Know The Madinah Mushaf Of The Qur’an Was Hand Written By One Man? from May 2019 is about the same scribe or calligrapher, i.e. Uthman Taha but does not mention how long it takes him to manually copy the Quran.
The article How long did it take a scribe to copy the Bible? claims, without citing a source,
It typically took a scribe fifteen months to copy a Bible.
This is quite a bit shorter than the time it takes Uthman Taha to copy the Quran, even though the Bible is roughly ten times longer than the Quran. The reason is probably that Uthman Taha is extremely careful in accomplishing his task, since his copies have been used as a source for printed editions, which appear to be facsimiles rather than typeset editions.
What I couldn't find out is how long it would take a scribe to copy the entire Quran, especially before print was invented. Has there been any research on this? If yes, what does it say about how long it took?