You're talking to someone who's fixed their microwave several times to keep it going 20 years.

Nah, antiques are stuff like the apple 2 or the amiga, it was a different world back then

15 years old is just old and has too little ram

Sure. But my needs haven't exceeded that RAM. I just want to keep doing the things I was doing for years on it happily, but security updates, broken services and website bloat have intervened.

Just switch to linux and it should just work. There are distros that use very little ram and it stays updated. Noscript can help you block javascript on websites

A 15 year old device can be still as capable as a raspberry pi and those work fine now for modern computing

"the things I was doing for years" unfortunately involves several native apps. There's a reason I got a Mac, after all.