Has anyone else had a bigger waste of money than that lately
In non covid times, I pay thousands of pounds a year for fresh air and to be taken out to sea to jump off a perfectly good boat (scuba diving).
I can afford it but I’m going without other (non-essential) things. There’s loads more I could be spending the money on that I’m always complaining I can’t afford - I wonder why
This is the key question for you. How you decide what you spend your spare money on after you've covered your essentials.
So as long as you have covered your essentials, and by that I mean rent/mortgage, bills, food, essential travel, pension, savings for annual and irregular expenses like insurance, replacement of white goods, car and car repairs, provision for loss of income etc it is up to you how you spend the money that gives you pleasure but, as you've rightly identified, there's only so much money available and if you find you're spending too much on one pleasure so you can't afford something else, that's when you need to make changes.
Because quite often, if you work out how to do coffee cheaper, you'll also be able to afford other nice things too - holidays, clothes, a nice car or save for a deposit for a mortgage, if that's your issue.
As you've realised, small regular purchases really add up. And food and drink out of the house is probably one of the most common ways to spend a lot of money on what seems like not very much and is also probably easiest to save most of that money, by just making it at home as much as you can. If you cut something down from daily to weekly, you're still having a nice treat, but you probably save about 2/3 of the cost, which frees up a lot of money for other things or to build a savings buffer, so it isn't a worry if your washing machine breaks, or the car needs fixing.
£4 a day, 5 days a week is £20 a week, which is over a thousand pounds a year, or about £12k in ten years if you got a bit of interest on savings. That could buy a nice car, or lots of nice holidays, just by cutting down on coffee.
If it makes you happy I dont really see what the difference between "I spend £84 on delicious and practical takeaway coffee" and "I spend £84 on two pieces of designer makeup" is
There isn't any difference. You won't have either in a few weeks/months but if you're in a position like the OP who might be saying 'I wish I could afford to buy nicer make up, or go on holiday, or fix my car, or put the heating on without worrying', or all manner of other things then being aware of the impact of her daily coffee and looking at ways to reduce this spend is a good place to start'.