Hi sethnerika,
If your 2012 MacBook Pro has a solid state drive inside it, as well as at least 8 GB of RAM, you should upgrade to the last supported OS version for your Mac - macOS Catalina.
macOS Catalina is still currently receiving security updates until October 2022, so that would be the safest option for now (since it's actively supported by Apple).
Before you upgrade to macOS Catalina, please note the following:
- macOS Catalina does not support 32-bit applications. You can check which of your apps are 32-bit by clicking on the Apple menu, holding down the Option key and selecting System Information. Once that app is open, check Software -> Applications.
- macOS Mojave and macOS Catalina use the Apple File System (APFS) format for the boot drive. This is an improvement for solid state drives (SSDs) but not for rotational hard drives (HDDs). All of your data will be preserved during the update and conversion.
To upgrade to a newer version of macOS, including macOS Catalina, download the desired installer from this page: How to get old versions of macOS - Apple Support