The proper way to reconcile the two reports from ʿUmar:

Once the reader sees how flimsy this narration from ʿUmar really is, there is no need to force a reconciliation between it and the sound report from him, as some have done when they claimed: “At first they used to stand for eleven rakʿahs, then they stood for twenty and ended with three as witr.” We maintain that reconciliation presupposes authenticity, and since these chains are not authentic, the proposed harmonisation is unnecessary. In fact, that very attempt can be countered. Al-Mubārakfūrī (2/76) wrote immediately after citing it:

“I say: Someone could just as well contend that they first prayed twenty rakʿahs and later prayed eleven. This seems more likely, because the latter accords with what is firmly established from the Messenger of Allah, whereas the former conflicts with it. So reflect.”

The twenty—if proven at all—was only prescribed for a particular circumstance that has now disappeared.

Moreover, even if someone remains unconvinced by the foregoing demonstration of the weakness of the ‘twenty’ attributed to ʿUmar, this still does not oblige him to hold fast to that number and abandon what is authentically established in the Sunnah from the Prophet ﷺ. ⦗69⦘