If I make a bootable pendrive running macOS, will downloaded apps and data persist on each boot?
Sorry if this seems like a basic question, but I couldn't find a clear statement on this anywhere: I wish to make a bootable pendrive running macOS Mojave, so that I can run some 32-bit apps. So I want whatever apps and data I download to persist on the pendrive, on each boot. Is this the case by default, when I use the createinstallmedia command on Terminal, as suggested in Apple Support, to create the bootable drive?
Solution 1:
The direct answer to your question is… yes. if you boot into a full macOS from any drive, it will behave in exactly the same way; all prefs, files, updates, documents etc will be kept, exactly the same way as it would from your regular internal boot drive.
However - and this is a big however…
running macOS from a USB stick will be so stunningly slow that you'll wonder if it's hung. Not only will it be slow, but it is so likely to glitch & fail without warning that it is absolutely not recommended.
If instead you use an external SSD over USB-3, then you will have a viable system, running at speeds comparable to a regular internal drive.
Also note: createinstallmedia creates a bootable installer, from which to install a full OS. You cannot use it directly to run macOS.
Solution 2:
The createinstallmedia command creates a startup disk whose purpose is installing MacOS onto another drive.
If you just want to install MacOS onto a USB thumb drive, then just run the OS installer app and select the drive as the target. (It will present you with the current system volume by default, but there's an "Other Volumes" button.)
Once you've installed the OS onto your USB drive, yes, it will be a read-write volume, so things will get saved there and stay there. (Though remember to keep a backup as thumb drives can fail suddenly.)
An alternative strategy might be to host Mojave inside a Virtual Machine (VM), which is "an OS as an app". So you launch the VM and Mojave runs in a window, inside your Catalina (or later) OS! Parallels or VirtualBox are the two main VMs.