Have you checked if you are running out of memory (RAM)? If you do so, the operating system may choose to write some of it to disk temporarily, and if this happens on an HDD, it might result in the freezes you describe. One way to check for this would be to open your task manager, and keep an eye on the memory usage, which you can increase by opening random websites in new tabs. Then, if the memory usage goes up and the computer freezes when it is around 90-100%, that is probably your problem.

Can you post HDD's SMART data?

To add to all the sensible things that have been said already:

A defective hard drive has been mentioned. While it is a possibility, defective hdd tend to quickly deteriorate more and more. Yet the situation seems to have been going on, all the same, for some time. Also, the OP says the computer is not that old.

To the OP: has the computer been moved around while working? A lot? That would lead to problems in the hard disk drive, fast.

How much memory is in the computer? Maybe some is being written in the hdd? (virtual memory)

Maybe a program in the background is doing some shenanigans? Like, trying to connect to something?

Is there any unsafe software in the computer?

...
Nice that you mention that. Indeed, it is better to eliminate the simplest possibilities first.

Could be a faulty HDD, did you try considering an SSD? it can help in a lot of these kinds of scenarios. 1tb drives how are pretty cheap so I would highly recommend advancing to a chip based storage unit for your everyday tasks. GL on your issue! :)

https://www.amazon.co.uk/Samsung-Internal-Solid-State-MZ-77Q1T0/dp/B089QXQ1TV/ref=sr_1_3?dchild=1&keywords=1tb+ssd&qid=1612113082&sr=8-3

I also vote it could be some kind of weird driver problem.

I had a problem in Windows 7 where it would sometimes suddenly just shut itself down. Not that often, but I had it happen like twice within a month or so.

First I thought it could be my laptop overheating and there being a critical temperature shutdown, but no, the temperatures were fine (and I wasn't really doing anything taxing at that moment).

Then I thought it might be power supply failing... but this was a laptop with a battery, so it didn't make sense the power would go off when there was also a battery available. Also, I never saw this problem on Linux on the same machine, so if it was hardware based problem like the power supply failing, I presume it should have affected both Windows and Linux.

I think I checked Event Viewer and saw some error code there, and googling for it, I found many other people had had a similar problem in Windows, and it was caused by there being several conflicting audio drivers loaded and enabled, and you needed to disable the extra ones.

I also had several, like five, sound card drivers enabled for some reason, no idea why, most of them were called something like NVidia HD Audio. I disabled all but one, at least so far I haven't had any problems.

To the OP: Does Event Viewer tell you anything?

How full (to capacity) is the hard drive ?. And is it a (mechanical) spinning disk type hard drive or a solid state (no moving parts/circuit board) type hard drive (universally known as an SSD) ?.

I'd wonder how much memory you were using. When you heavily exceed your ram (but are using Virtual Memory) a huge amount of time may be taken doing swaps.

I remember one computer i helped with a Windows 98/ME machine (2010?), where they had like 300Mb ram, but had 500Mb of applications loading at boot. Took more than a half hour killing applications and killing services before it ran at normal speed, then i recommended they only have 1 application open at a time.