On the Documentation page, many of the linked resources appear to be outdated.

Under "Getting Started":

• The official FAQ says the examples have been run using Ruby 2.3.
• poignant.guide doesn't give a version number I can find, but the GitHub link says it has "Updated code examples to match Ruby 1.9 behavior".
• Ruby Essentials on techtopia.com, under "Getting and Installing Ruby" shows ruby 1.8.1 (2003-12-25) [i386-linux-gnu] as the sample output.
• Learn to Program by Chris Pine says "What's here on this site is the original tutorial, more or less unchanged since 2004", though it also links to a textbook which you can buy with a 2021 publication date.
• Learn Ruby the Hard Way, clicking through to the web version gives an SSL error, but I can manually switch to HTTP. Then it shows ruby 2.1.2p95 (2014-05-08 revision 45877) as the sample output in the setup chapter. There is a Google screenshot which looks like it's also from ~2014 and shows the same version number.

Under "Manuals":

• Programming Ruby says: "This book documents Version 1.6 of Ruby, which was released in September 2000".
• The Ruby Programming Wikibook shows ruby 1.8.7 (2009-06-12 patchlevel 174) [i486-linux] as a sample output for ruby -v, and the Overview page refers to a feature which "will disappear in 1.9" in the future tense. Those two pages were edited in 2022.

It's possible some of them might be up-to-date despite old version numbers in sample outputs or screenshots. At least, none of the linked pages explicitly say they are accurate for Ruby 3.0 or later. For a new Ruby user (myself) this didn't inspire confidence that the information on those sites would still be accurate.

I was suggested to post this as an issue by @zenspider in the Ruby Discord server.