Just want to add my 2 pennies...
While any manufacture's Home User Class computers are usually found lacking both in quality, longevity, and support; HP's Z Series Business Class Workstations are top notch in quality, longevity, and support.
HP continues to offer phone support, and releases BIOS updates and security patches, for systems 8+ years old. e.g. The HP Z420 was first manufactured in 2011 (Sandy Bridge CPU), and had at least 3 BIOS updates in 2018 and 2 in 2019 to address security vulnerabilities (including Meltdown & Spectre). With most other manufactures, you're lucky if you get 2-4 years of BIOS updates (which includes Gigabyte, ASUS, and any of the cheap home user class brands), let alone any phone support.
Unless something has changed recently that I am unaware of, Dell's Support will not even talk to you without an active hardware warranty or service contract; whereas HP will always talk to you and give you support regardless of an active hardware warranty or service contract.
I used to be die-hard Dell, and still prefer their PowerEdge Servers over HP's, but as for Business Class systems I've completely switched all my clients to HP's Z Series Workstations / Laptops.
I'm only posting this as a difference in my experience and opinion.
When stating your opinion, you can't just say things like "Dell is a better company, and have much better warranties" or "with HP, their lack of manufacturing craftsmanship, insures their computer's don't last anywhere near that" as if it is a undisputed fact.
The truth is that ANY Business Class System should last 10-15 years without issue, barring that the user is following Best Practices and using an AVR UPS (regulated clean power).
The only reason most people using (for example) an HP Z240 or Z420 with a Xeon E3 or E5 with 64BG of RAM are having to upgrade to something newer, is because of the EOL of Windows 10 coming in October of 2025. Of course, if they are using Zorin (or any nix), an HP Z230, Z240, Z420, Z440, Z620, Z640, Z820, or Z840 will have more than enough power for years to come (of course they'll need a decent graphics card).
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TL;DR
As far as the OP, I would agree, it would appear be be a possible hardware issue. However, it could be related to Graphics Drivers (especially if using NVIDIA). It could also be an issue with Wayland, which I would recommend against using.
As far as the possible hardware issues:
It could be any of the components, but I would start by testing the memory with memtest86+ https://memtest.org first.
If the memory is good, I would try stressing the CPU or GPU.
GPU: Unigine Heaven (or Valley)
CPU: I don't have a preference...
If all of that is good, it could be the motherboard or power (supply or battery) related... (which is harder to diagnose)
It could also be overheating, which could be a bad fan, poor ventilation, etc. I would download a temperature monitor like Freon (recommended), psensor, or TopHat (GNOME Extensions). I use all 3.
I would also recommend replacing the Hard Drive, if you haven't already (I always do this with any Drive after 5 years of use).
Hope that helps! 