On the whole money isnt/is legally shared money. Its not a simple answer, really is it?
When a wage goes to someone it's their money. They may choose to share it. Have it paid into or move over to an account accessible for both. As long as both people (regardless of who is working and who isnt) see it as shared, it is.
However, the second one person decides not to make their wage accessible to the other, there no legal obligation for them to do so. In the event of divorce, assets and money will be split. But that doesn't mean the person's wage has to be accessible to the other person until the divorce.
You could have a family where both people work. One 100k one 40k. They have always shared. The higher earner decides they will cover the bills (or their usual portion) but not keep the rest. There isn't much the other can do but decide wether they want to divorce/split. or only cover half the bills. Or lots of different things.
In the event of a split the divorce can go several ways, especially if one is a high earner. But often the house would be sold if the lower earner, can't afford the mortgage. But not always.
On the point about it being exhausting to think about what happens when you split. It's not really. You think about it when big decisions are being made. Such as house purchases, investments, wether to have more children. Its no more exhausting than than planning for one person's death or illness.
I am a higher earner, who doesn't really share money. But we aren't a wohp/ sahp set up. I pay a bigger portion of bills, pay more money to the joint. Then what's left over is mine.
Difference is I refuse to marry because I don't wish to financially tie myself to someone. We don't have joint children.
During the pandemic when dp was made redundant, I paid all the bills made sure do had the free money that he would normally. We tried a joint account but he hated dipping into it. He didn't really like me transferring it either. Because he doesn't want to share finances either. The house is mine and when dp moved in he kept the ones from his house and invests it, so if we split and he needs to rehouse himself he can.
In the event of my death, he also gets a pay out. But all my personal assets go to my kids.
Holidays, eating our etc arent really an issue because we don't have extravagant tastes. One or the other pays. I have put more into holidays when I have wanted to upgrade flights or rooms.
I will be supporting my dd and my ds through uni soon, alongside them working. Dp obviously won't be contributing to that.
It suits us. We enjoy life. And I know if dp leaves tomorrow, all the bills will be paid and we will be fine. My priority is always going to be my children. Not DP.
Though in some splits, the higher earner often sees it as paying to their ex. Rather than paying for the children. And that's where problems arise.