I have a mac book pro (retina, 2012) what is the latest system I can run on it?

And to reach Catalina follow this How to get old versions of macOS and verify what version this computer Qualifies to install.  For Best results use Safari to commence the download as Others may not work.

Suggest using Go64 to find 32 bit application before attempting the upGrade. Some or many of the Application already installed may required update or upGrades to 64 Bit Versions.

Make Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS

Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina & Big Sur supports only 64 bit and there is no workaround.

Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation

Catalina 10.15.7

These Mac models are compatible with macOS 10.14 Mojave and 10.15 Catalina:

• MacBook (Early 2015 or newer)

• MacBook Air (Mid 2012 or newer)

• MacBook Pro (Mid 2012 or newer)

• Mac mini (Late 2012 or newer)

• iMac (Late 2012 or newer)

• iMac Pro (2017)

• Mac Pro (Late 2013)

For Mojave only:

• Mac Pro (Mid 2010 and Mid 2012 with required Metal-capable graphics card–

https://support.apple.com/en-us/HT208898)

❗️– IMPORTANT! – 32-bit apps won’t work in Catalina. Use GO64 to check yours.