It's difficult to separate the effects of COVID from the effects of BREXIT. Since 2019, it looks as if England has done slightly worse than the EU, but very slightly better than France. BREXIT has become less popular in England.
I suspect England's problems have more to do with poor quality British politicians than the other effects of BREXIT. I watched some videos of Parliament in session in 2022 and it was comical, one person speaking to mostly empty seats.
The United States workforce is 170 million out of a population of roughly 330 million, over 50%. As I illustrated above, the median household income of $84,000 is more than enough to meet your criterion for a good job. Thus more than 1 in 4, not 1 in 5, have good jobs.
It is not reasonable in this context to consider children, who are 26% of the population. The figures then become 170 million out of 244 million, or 70%, thus 35%, more than 1 in 3, have "good jobs." Then figure in retirees, who are also irrelevant to the job market...
10 million is sufficient to assure genetic diversity.
******
As a point of comparison, assume everyone dies at age 80, starts working at 20, retires at 65. That's 43.75% of the population not working, or by your figuring 1.688 people working to support 3 people. Initially, that sounds like an excessive burden, but it requires a closer look.
Median household income in the U.S. is $84,000. FWIW, that includes single parent homes, and I don't know how to factor that into calculations.
In a non-nanny-state society, everybody is responsible for himself and the results of his actions. His responsibilities include supporting his children until they can support themselves. That need not be an overwhelming cost if it were not for the excessive costs of education. (For 2 children in the U.S., kindergarten + 12 years grade school + 2 years college at $20,000/year is $600,000. {Thanks, teacher's unions.} 20 years food for 2 children $100,000. Incremental rent for a larger apartment or the incremental cost for a larger house, $100,000. Other costs are usually small in comparison. That's $900,000, 2/3 of which is government-mandated education. In a free market a better education for 2 children could be provided for about $120,000, bringing the total to $320,000.)
From 65 to 80, a person should be living off what he accumulated during his working years, (In the U.S. 45 * $84,000 = $3,780,000 gross, minus expenses.) That is not living off someone else's production, that is living off the surplus created during a lifetime. A person is not being supported by someone else when he's sleeping or on holidays or weekends. All that changes in retirement is the timescale.
Taxes and support provided by government do not change the financial principles involved, that should be "money in" = "equivalent to money out." But government is inefficient, and that's a problem.
In summary: A lifetime income of $3,780,000 to support rearing 2 children for $320,000 to $900,000 leaves $2,880,000 to $3,460,000 for a couple to live from age 20 to 80. This should not be a problem or a reason not to have children. Arguing that it takes X people to keep Y people alive is pointless. Over the course of history, production becomes more efficient due to technology, meaning that it will take even fewer people to support 3 people at the same level of well-being, and that's a good thing.
The scriptures of all the Abrahamic religions have substantial elements of death cult ideology. They vary in how much attention these passages get in modern times, mostly it's ignored except by some malevolent leaders.
Because the "holy" books are more or less static, there's always the risk that the death cult aspects will be brought to the fore again. Our best bet for survival is rational education.
I've known people who behaved in an evil manner because they thought it was fun. None of those people misbehaved because they were mistreated, they misbehaved because they just weren't caught and punished. Lacking punishment, they continued misbehaving, even bragging about it and encouraging others to follow their lead.
Most human behavior depends on feedback.
Human beings were created by water to transport it uphill.