The computer I built in 2011 lasted until last summer. I smiled widely when I came to tell my wife and my friend, where my friend then asked why I was smiling when my computer no longer worked.
"Because now he can buy a new one" my wife quickly replied 😁
I'm rocking a Ryzen 2700x since 2018, or early 2019, and it's still working like a champ. Granted Cities Skylines 2 is a bit much for it but I've been playing Baulders Gate and Helldivers with about a 100 fps average.
5700x,5700x3d may be an upgrade path with your existing mobo. They were $100-190 a month ago.
How big was your city when you noticed performance issues? I'm near or at 100k on 5700x3d and can play at 3x speed smoothly. When I had a 2700x I noticed lag a lot quicker than 100k but that was much nearer to launch.
Mine is from 2011 and still going strong. It had some upgrades like extra ram, ssd and a new gpu a couple of years ago and I had to replace the front fan. It starts making a horrible noise about 4 hours into a gaming session with a graphically demanding game, but apart from that it runs perfectly fine. I don't really play demanding games usually so I don't really care. When it finally dies, I might just swap out the motherboard and cpu and keep the rest. It's my personal ship of Theseus.