Useful tips really. Just for completeness – these procedures also work with High Sierra and Mojave.You are correct in saying that it (195.x.x) also available through Mojave and High Sierra security patch.
but am just explaining the easiest way to do so. Because it would be easier to install Catalina directly compared to installing Mojave or High Sierra and installing security patch after.
To get 195. , you dont even need to install Catalina to the Internal OEM SSD (if you wish to retain the data in that ssd, assuming you are borrowing it from someone). You can simply plug the OEM ssd inside the macbook. And install Catalina to other external drive plugged through USB. It will still update your BootRom, as long as it detect that there's OEM SSD inside the macbook.
If you are already in 195. , regardless your OS version, you can went up to Monterey directly, even with 3rd party ssd.
While a new OS offers advantages in security, some people may have good reasons to want the 32-bit compatibility of the older OSes.