If I have Linux installed on an SSD and I plug it into a Windows computer (a PC which I did not use to install linux onto the SSD), would I be able to use linux in that PC from the SSD?
No, they would not have driver issues "for sure". It will work just fine most of the time and you can prepare the ssd for hardware that has problens withnlinux in general like some wireless chipsets.
Well that's my point. Like if you take a completely unprepared desktop install you'll likely run into issues with things like wireless chipsets, Nvidia graphics, etc. I think using UUIDs in /etc/fstab is the default nearly universally now, but if not or if OP changes it manually they could run into boot issues with that. Also grub.cfg for similar reasons.
Also have to consider EFI vs Legacy, secure boot, etc.
Yes, but with some preparation. First, secure boot has to be disabled. Then you need a FAT32 esp partition on your SSD which has to become the system boot partition. Easiest way is unpluging all other hard drives and ssds and tgen installing the linux distribution of your choice to the ssd. You can install different drivers for all circumstances, it is for example no problem to have drivers for AMD and NVIDIA GPUs installed, only the right one will be loaded. You can also optionally prepare your ssd linux for mbr systems if you want compability with really old systems. Archwiki has a good article about that iirc.
Should word provided the PC is EFI/UEFI enabled and theres an EFI partition for the linux install.
In fact thats exactly how Pop_OS handles it. So, my system uses a single drive, but i have EFI paritions for linux and windows. THe fact that its a single drive or multiple doesnt really matter there.
I’m going to play around with it soon by installing full Linux onto an external SSD. I’ll let you know how it goes. I’ve seen some guides and tutorials that mention that it’s possible.
Should work, provided you can access the bios to choose it as the boot device. The usual issues with this are: 1. It's a school / work PC and BIOS access is locked 2. It has weird hardware and you can't get network access working to sort it.