Steam users of RimWorld usually don't have to be concerned about running the latest stable version of the game - unless Steam glitches or they forgot they opted into a beta branch, that is. Non-Steam users (or anyone without auto-updates) though, can easily miss game updates, which can cause severe issues especially when also using mods!
In general you should always keep your game updated. You'll gain more from new fixes and improvements than you'll lose, and using mods demand it anyways. While some mods survive minor patches, the entire mod-ecosystem - especially key frameworks and big, popular mods - is built and tested against the current stable release version, so running an older version (or the unstable branch) almost always breaks compatibility.
First you have to find out what even IS the currently latest-stable version of course which can be achieved in a lot of different ways with different levels of viability. Here's a list of the most important methods with relevant links to them:
The #builds channel on the Ludeon Dev Discord (but you might need to filter out the stable releases from patches on the unstable branch)
RimWorld's Steam Community News page or SteamDB, but those sources can at times miss info about minor patches
The RimWorld Wiki has a page on versions of well, but is at times not properly updated
GoGDB.org has info about the latest updates, including the version-number and is usually in line with the latest version on Steam
The most reliable method probably just is to ask the community, like on the RimWorld Community Discord
After you've found out which version is the current one, you might next want to check which version is running on your end. To find out about that, you can use any of the following methods:
The game shows the exact version-number in the top-left on the main menu
If for instance you're unable to load into the game at all, you can also check the Version.txt-file in your install-folder
The version-number is also part of any Hugslog or Player.log-file in case this is easier to access for you
Whenever you find yourself running anything but the latest version of the game, make sure to prioritize updating first. Especially if you encounter errors/bugs you don't even have to ask for troubleshoot-support - every experienced troubleshooter will ask you to update your game first anyways.