What is the Biblical basis for the husband being the main/(sole) provider?

The role of leadership is spiritual and the role of provider is material. Before we go any further we should put 1 Tim 5:8 into context to establish the principle involved. Here is a partial quote [1] from a relevant article:

Paul is stating negatively the truth he had just laid out in verse 4: “But if a widow has children or grandchildren, these should learn first of all to put their religion into practice by caring for their own family and so repaying their parents and grandparents, for this is pleasing to God.” Children are to take care of their parents and grandparents. Those who fail to provide for their relatives are worse than unbelievers in that they are not living out their faith. Paul repeats this principle in verse 8 because, apparently, many in the church at Ephesus were violating this command.

The phrase’ Anyone who does not provide’ in 1 Timothy 5:8 is a first-class conditional statement in the original, which could be better translated as “When any of you does not provide” or “Since some of you are not providing.” The word ‘provide’ is from the Greek pronoeo, which means “to plan before.” It indicates that forethought is necessary to provide care for one’s family.

If a stay-at-home dad is shirking his duty to provide for his family, then he is sinning. Failing to provide or plan for the needs of his family makes a believer guilty of two things. First, “he has denied the faith.” This does not refer to the loss of personal salvation. Paul here is not judging the ultimate destination of the soul but current actions. A person who refuses to provide for his family is living contrary to what he says he believes and has denied the principle of compassionate love at the heart of the Christian faith (John 13:35; Romans 5:5; 1 Thessalonians 4:9). In other words, the real command here, for stay-at-home dads and for everyone, is that there must be no contradiction between faith and conduct. URL: https://www.gotquestions.org/stay-at-home-dad.html[1]

The Bible nowhere says that women are not allowed to help to provide financially for their families. Take, for example, Lydia, a dealer in purple cloth from the city of Thyarita, who was a worshipper of God (Acts 16:14). What the Bible does say is that it is the primary responsibility of a man to provide for his family, and that includes his parents. 2,000 years ago there was no welfare state or social security. Aged parents, widows and orphans were dependent on help from their families or nieghbours. That is why Paul made this point – for Christian men to set a godly example.

Religion that God our Father accepts as pure and faultless is this: to look after orphans and widows in their distress and to keep oneself from being polluted by the world (James 1:27).

There is no condemnation or shame if a man is physically or mentally unable to make financial provision for his wife and children (if he has any) or his aged parents (if they are still alive). What is condemned is wilful and deliberate abdication of responsibility.

Neither is there any conflict if a husband and wife agree to share the responsibility of earning an income and taking care of the children and their home. In this situation, the husband continues to provide spiritual leadership as well. But he could not lead if he was wilfully abdicating his responsibilities to provide (materially) for the welfare of his own flesh and blood. Such a man would not deserve respect and could not expect to become a leader in the church.

Of course, a man does not have to be married in order to hold a position of authority and leadership within the Christian congregation. That is not compulsory!

EDIT: This question has just been change by the asker to mean something completely different to the original question. It's called "changing the goal posts".