Would Umar ibn al-Khattab's—may God be pleased with him—going alone to a blind, old woman to clean her house and provide for her needs be considered impermissible seclusion (khalwa) with a non-mahram woman without lust, or not?

The matter is as stated in the fatwa regarding the impermissibility of khalwa (private seclusion) with a non-mahram woman, which is a principle established by authentic texts. Anything to the contrary is incorrect or is interpreted as applying to a situation where it was necessitated, such as by an exigency or a need. If the story of 'Umar is authentic, then it must be understood in the context of the absence of suspicion and the safety from fitna (temptation), such as the woman being elderly or someone else being with him. It is authentically narrated in Sahih Muslim from Anas that Abu Bakr and 'Umar visited Umm Ayman. Al-Nawawi, in his commentary on this hadith, mentioned the permissibility for a group of men to visit a righteous woman and listen to her speech.