Michel Corbin wrote:
Thank you for the thorough response. I realise it’s best not to fool around with Apple’s structure. I will create short cuts inside the key folders (Pictures, Movies, Documents) to point to the external drive.
That's not going to work.
If your data doesn't fit on your external hard drive, the only official, and well-supported solution is heavy use of iCloud with "optimize" settings enabled. Even then, I strongly advise having one machine that does not have any optimizations set so that it can download and backup the entirety of your data. This will require a monthly iCloud fee and also perhaps the cost of another computer/hard drive to keep the data downloaded and backed-up.
Failing that, having your entire home directory on an external drive is the next-best solution. Nothing that HWTech said is wrong, but this is a solution that should be expected to work. The key is that you can't expect this to work and also expect to always be on the bleeding edge of any software update. To be clear, anyone currently running any version of macOS Ventura is on this "bleeding edge". Back in those 12.5.1 days, macOS Monterey was that bleeding edge. Anyone who valued their data in any way would have been running Big Sur back then.
Currently, it is very unlikely that Apple would make any change to Monterey significant enough to break a home directory on an external volume. But in any event, moving your home directory to an external volume is an advanced option. You can expect regular problems, especially with 3rd party software. You also have to be careful about mounting the external volume. Either manually specify the mount point and/or make sure to enable ownership on the volume. This isn't normally done, so you are on your own in such a configuration. Don't attempt it unless you are confident in your abilities to correct any problems on your own.
But in spite of all of these complications, any attempt to use aliases, links, etc. is a guaranteed, hard fail. These will not work and will only corrupt your data.