Is it safe to install iPadOS 18.5 on my iPad Pro M4?

I think iOS 18.1.1 resolved whatever issues people were warning about with 18.1. My 13-inch M4 iPad Pro has happily run every version of iOS since then, including 18.1 and 18.5. Yes, some fraction of users do experience problems with essentially every update, if only because devices have different update, contents, and usage histories.

If you wait for a perfect release you will be waiting a long time.

iPadOS 18.5 is both stable and current - and, essentially, includes important security and functional updates for your iPad.

Unless you have a very specific reason not to do so, such as avoiding a known issue with a critical App upon which you have reliance, you should always apply system software updates where available. Otherwise, you may unwittingly leave your iPad and other devices vulnerable to discovered security vulnerabilities and developing exploits.