To get your F12 key back for other shortcuts, stop Tilda:

killall tilda

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

To prevent Tilda from starting on boot you can remove it

sudo apt-get remove tilda

or disable auto start:

• Go to Mate Control Center > Startup Applications
• uncheck "Tilda"