I have a bit of a saying...
"An old computer will perform the tasks it was designed to do as well as it did when it was purchased."
So, a computer that ran Windows XP like a champ will still run Windows XP like a champ. It's just that Windows XP isn't really a viable choice as a modern operating system.
There is some leeway. We're currently in a CPU "paradise", where a CPU 10 years old will happily run current Linux. Heck, it'll happily run current Windows 10 (or 11, if you can tell it to bypass the TPM 2.0 check).
But, these old computers aren't really worth using for modern tasks. They're great for doing what they were designed to do, but to do modern tasks with them would just be an inefficient waste of resources (such as electricity). It will cost you more money to do the same amount of work that you would do with more modern hardware.
I'm actually a big fan of retro computing. I just don't think we need to consume more resources unless we absolutely have to.
You're trying to do modern tasks on a system that's pretty old (if I read enough of the thread). It may not be reasonable for you to pick up a $100 refurbished computer, and I can relate to that. But, that $100 refurbished computer will be a much better experience for you and will be so much more efficient, meaning lower power bills.
Those power bill increases add up and they add up quickly. I once did the math for a Pentium 4 vs a used i7. Performing the same load on each would mean that in about a year and a half was the payoff time. The P4, over that year and a half, would cover the cost of the used i7 (in that instance).
Retro computing is great. It's a wonderful hobby. I'm not sure that I'd try to use an old system to accomplish meaningful tasks, especially online tasks, unless I absolutely had to.
Of course, if it's just for fun, have fun with it. I mean, sure, it's more energy but there are other hobbies that use far more energy than this one will.
That's a bit of a novella, but I wanted to make my thoughts on the matter reasonably clear.
By all means, keep doing what you're doing. Don't let me stop you. I'm merely sharing my views, which could easily be from a position of priviledge.