See also: https://www.bbc.com/news/business-48993008
which as well as explaining the background to the note and debates over whether it should be taken out of circulation also points out the context the average British adult was making about 20 cash transactions a month as of 2018 (none of them involving £50 notes)
https://en.wikipedia.org/wiki/United_States_five-hundred-dol...
https://en.wikipedia.org/wiki/United_States_one-thousand-dol...
https://en.wikipedia.org/wiki/United_States_five-thousand-do...
https://en.wikipedia.org/wiki/United_States_ten-thousand-dol...
Your best bet of happening into a $50 is if you go to a bank for an in-person withdraw and they ask you for preferred denominations. Generally the money is dispensed in $20s even there unless specified.
Your second best bet would be if you're selling something "on the side" and the purchaser uses a $50 in a transaction, which I would say is also rare these days, most people use Venmo or equiv.
Your best bet of handling a $50 is probably as a bartender, or of course as a bank teller.
I have held $50s a few times in my life, and even my reaction is "huh, a $50, don't see those often"
Nowadays that's less common from tourists from Europe, but tourists from Asia are still likely to bring cash.
Let me introduce you to a $2 note.
They are effectively becoming the new $20 with inflation continuing upwards, and I expect their popularity to continue to increase.
A friend's dad showed me one when I was at school - that's it. He seemed amused I hadn't seen one before, then after making a minor show of it, as if it was some precious, rare item, said he'd never previously seen one either. They've been uncommon my whole life, and apparently could/can be difficult to actually use, shop assistants being unfamiliar with them and not confident in their legitimacy.
I expect today most people would use bank transfers for the sort of sum where the sheer number of notes would make a £50 one useful.
But when the bill is £45, there's no problem anyway.
I felt like I was very cool considering how rare they are.
(Maybe they're a bit easier to get hold of now, especially with recent inflation? But I don't use cash as much as I did when I was younger.)
I have had many places reject $100 bills though.
I’m that weirdo that tries to pay cash for most everything, so sample size is large and across a diverse set of businesses.
Due to what I tend to pay cash for these days (lunches, drinks with a friend, etc.) and prices being what they are, they are rapidly becoming my “go-to” denomination.