As in, pay isn't the problem. Your feature requests/bug reports/whatever would not be handled any quicker if you tried to give us money for it (which people have tried to do).
I repeat, it's a 3-weekends-a-year spare-time project. I'm OK spending that amount of time on it, because sometimes I feel like doing so. No realistic amount of money is going to make me want to spend more than that, though. And sometimes it doesn't happen for other reasons.
For example, I usually take some time off around Christmas, and _usually_, 1-2 weekends around that time I spend on stb lib maintenance, because I'm on vacation anyway so it's not a context switch from work, and the weather is usually miserable where I live around that time.
2023 that didn't happen because I badly sprained my ankle early Dec and then got a cold in early Jan, so all my winter holiday time end-of-2023/early 2024 was spent being sick in some form or other.