Mac OS Catalina

If it has an SSD, then it should be fine.

If you have any third-party system modifications, then you may have problems with those as they are often poorly written.

What OS are you currently running? That will have some effect on how easy it is to transition.

If you have any 32-bit applications, they will not run in Catalina. There isn't any magic trick that will make them run in Catalina.

You can review what 32-bit apps you have and what options you have to update them with Go64.

Catalina is fine. Lagging and crashes are almost always caused by poorly written code contained in third party apps. The biggest offender is anti-virus software. If you have any installed... uninstall it immediately.

If you are running Mojave, then you already know how laggy or crashy it could be. Catalina ran better than Mojave on all of my Macs.

Upgrading macOS without fear - Apple Community

I'm a new user to MBP & don't have much knowledge in the OS. Is there anyway to convert all applications to 64 bit versions for free.GO64 didn't work.

That was up to the developers to do. They've had nearly 15 years to accomplish the task. If they have chosen not to do so by now, I would guess they have no interest in doing it at all.