Out of memory after half hour of use

I have a desktop with 32Gb RAM and Zorin 16.1 with windowing X11

After a while in use, Zorin freezes or certain apps won't load (VLC for example). Looking at logs it reports out of memory.

Zorin itself reports 31.3 Gig RAM

Firstly, are you using HDD (Hard Disk Drive) or SSD (Solid State Drive)?
Did you install Zorin manually or did you let it install automatically?

What is the output of /var/log/messages?

Zorin boots from an SSD drive installed from a USB live iso in the usual way. I must say that on bootup, Zorin displays a list of 'failed' actions but I assumed these were 'normal' as finally loaded and runs fine. It also updates automatically OK.
I do notice another oddity. The supplied Archiver often has issues with different archive formats such as 7z, multiple RARs and so on. I installed Pkzip Desktop which, with a bit of fiddling can usually sort it out, but I must say the Linux handling of compressed files leaves a lot to be desired. Usual it says the archive is corrupt but another archiver opens it fine but the Pk7 desktop won't open the archive directly it has to be extracted somewhere. All very confusing as I am basically a Windows person. No windows on here though.

I've also used Mint but somehow it didn't gel with me. Any suggestions for another ditro please?

Which USB installer did you use? Balena Etcher? I used Balena Etcher to install Zorin Education as it is over 5 Gb (My preferred install method is by DVD). It was to a Crucial SSD and it appeared to install fine then kept freezing. I had to abandon it in the end and installed Windowsfx 10 free edition. If you used Balena I suggest you try Ventoy first (I couldn't be bothered to do that as it would have meant digging out my Windows 7 Pro 64-bit drive.)
If you want to try something different then give Devuan 3.1.1 a try. I only downgraded from 4 because it didn't pick up my second monitor. It's my daily go to, using Plasma (KDE) desktop. I added tiled menu to make it look like Windows 10 but I've changed it completely recently.

I sometimes login to my LXQt desktop on Devuan:

Other distros to try are MX-Linux, Feren OS.

From a security viewpoint and sound viewpoint I'd always choose Devuan as it uses SysVinit over systemd and I can block pulse audio in favour of the superior ALSA (Advanced Linux Sound Architecture).
One thing I don't use in Plasma, is Kmail. The Anakondi backend crashes randomly. I prefer Evolution over any other mail client. I don't use Thunderbird as it is too embedded to Google. My next task is to change Firefox which is kept afloat mainly by Google. Devuan comes with Firefox ESR (Extended Service Release) by default which means you can lock it down - you can't do that with the standard Firefox. I refuse to use snapd or Red Hat's flatpak; they aee both bloatware.

Addressing the 7zip issue I don't have any issues using Archive in Devuan 3.1.1 with Plasma (KDE) desktop environment.

I would always advise Manual Partitioning:

  1. EFI/ESP 512 Mb FAT32
  2. 80 Gb root partition (/) Ext4 FS
  3. Whatever space is left use for /home formatted to Ext4 FS

You don't need swap area or even a swap file for SSD. And don't set up TRIM as this can lose data. In the old days I would have recommended non journalling system such as Ext2 FS but I sought help fro local Linux User Group and one member has had SSD with Ext4 running for six years without a glitch.