I read Floornight because of this post and it was very good.   So, there was at least some benefit to making this fanfiction.

It's worth keeping at in mind that people are currently unable to use the advantages of working from home to replace lost camaraderie because of the virus.  At the very least, it's much harder to do so.  This is important for the broader effects on human happiness, if not on the effects on work itself.  Once socializing in person isn't dangerous, people can use the hours of the day they save from not commuting, plus all the time they spend in neutral social interactions in the office (which are net negative because they take energy and time without providing joy), and use that on positive social interactions with people they actually like.  I suspect this will be a strong net positive for human happiness, because (white collar professional) offices are a lot more about controlling workers than efficiency and there are a lot of jobs that don't lose or even gain efficiency from not being in an office.

Plus, people are taking care of their school-age children, trying to arrange grocery delivery, working without organizations that might not have had a WFH plan ahead of time, trying to not die of COVID, and dealing with an unusually tumultuous political scene at the same time.  I'd urge caution attributing any particular effect solely to working from home.  Two years from now we'll have better data.

(I can say anecdotally (I know, I know) that working from home has improved my performance and cut the time I need to actually do my work down to a few hours a day, and my direct manager agrees with me on the first part (I have not shared the first part but I'm pretty sure this applies to everyone on my team and we're tacitly not talking about it lest someone feel obligated to ruin it).  I'd be going insane if I didn't have several good friends as roommates who are now home and able to hang out during the work day, but that won't be an issue once I could go hang out at a coffee shop, park, or other person who's WFH's house without risking the plague.  And I get to spend two extra hours a day, five days a week, at leisure due to not commuting - an excellent boost to both my health and happiness!)

Give it to an existing EA group or groups doing good work, like Givewell.  They probably can't absorb $1bn immediately but they could use tens of millions, certainly.

You also have to balance out all the people will stop doing work that benefits society with the group of people that create something of huge value in the they used to spend doing wage labor.  Traditionally it was rich people who therefore have a lot of free time that made all sorts of advances in science and mathematics (see all the lords hanging around 18-19th century science).  The same logic goes for forming businesses unless a massive percentage of people don't work - it takes a ton of money to start a business because you still need to eat before you're profitable, and UBI takes some of the strain off that because, at worst, you still have your basic income to fall back on.  It doesn't take many people doing extremely high value work of this sort because they aren't doing wage labor to make up for any number of people who sit on the couch and watch television all day.