>This is the most plausible hypothesis

It's not the most plausible hypothesis. Men are more likely to own firearms than women are, therefore they're more likely to attempt suicide by firearms.

How does that explain that this male vs female ratio stands in countries with low gun ownership rates?

I've been curious about the phenomenon of suicide for a while, so I've read quite a bit about it in different countries. One of the interesting things about suicide is the means of suicide is always whatever is most available or readily available in the environment. In the U.S. where guns are more available, about half of all gun deaths are suicides, and about 80% of those are men. But in some countries in Africa, men kill themselves more frequently as well, and the primary mechanism is by drinking pesticide.

My mental model is that men tend to be more extreme and less conservative than women (risk-taking is more prevalent), and this leads to more extreme approaches in how they try to kill themselves.

But it's been a while since I've read any of these statistics, and I have no special credentials. Just thinking about what we're observing.

Nonsense, that is an America-centric attempt at making up a narrative. The sex differences in suicide outcomes are essentially the same in countries with low to zero firearms ownership, eg Europe, Australia, Japan. If there are no firearms available, then other almost equally lethal methods are used (hanging, trains, etc).

The sex difference in completed suicides is nearly universally 3-to-1 to 4-to-1.

Top suicide methods in my country:

hanging/strangulation (9,164, 49%);

self-poisoning (4,098, 22%);

jumping/multiple injuries (2,423, 13%).

All three are equally available to men and women and anyone else.

In terms of rate, male suicide rate 17.2 per 100,000. Female suicide rate of 5.4 per 100,000

London has the lowest overall rate of just 7.3 per 100,000, 65% of the national rate. North East being highest at 14 per 100k.

The highest population group being Males aged 50-54 years, being 27.9 per 100,000

Wales is even worse, with Males aged 45-49 years being 32.3 per 100,000, and overall 21.6 (male) // 7.5 (female)

Generally the worse the economic opportunities, the higher the rate. Middle aged men are most at risk, men in general are at high risk, and guns have nothing to do with it

Even controlling for that the pattern holds.

effect still remains after you look at statistics in countries with low firearm ownership

Gunshot suicides account for 2.5% of suicides in England and Wales [1].

Try again.

[1]: https://pubmed.ncbi.nlm.nih.gov/15834784/