This is super stupid:

• In the Thunar file manager, select the file
• Go to File / Properties / Open With (WTF!)
• Select the preferred application from the list and hit "Set default"

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

• Prevents you from data breaches and liability risks
• Upgrade at your own pace
• Works with modern Rubies

Read more Show archive.org snapshot

This setting will apply to all files with that extension.