64 bit

Apple computers have been 64 bit for many years. You are seeing warnings about apps not being 64 bit. If you have 32 bit apps installed they will no longer work after the next operating system upgrade. If you do not upgrade your operating system beyond Mojave all your 32 bit apps will continue to work.

This is a generic warning only. You have to do nothing, 32-bit apps continue to work on Mojave and High Sierra.

In the future release of macOS 10.15, applications will have to be 64-bit. App developers will issue updated apps if they want their apps to work on these future releases.

32-bit app compatibility with macOS High Sierra 10.13 ... - Apple Support

https://support.apple.com/en-us/HT208436