Is it worth to buy iMac Pro 27" (2017 A1862) in 2025?

I would not buy an intel mac anymore, in a few macOS versions intel cpus will no longer be supported and your mac will be stuck on an old macos version.

Just to add, for that amount of money you could purchase a brand new M4 Mac Mini and a decent 27" monitor, which will outperform an iMac Pro.

Nope, I'd pass and buy a new Mac Mini.