KDE is one of the more resource hungry desktops, not the worst. But if you have a browser open with multiple tabs and other apps open you will sometimes run out with 4gb, at 8gb you should be fine. Hopefully that all in one can be upgraded easily, some are not. How much swap do you have?
YES and even 16GB is it worth to think about. the price-differenc isn’t worth to keep on low RAM-level.
With 8GB your fine but that’s the basic minimum if you want to run without too much compromises. 16GB and above will be perfect.
Looking at the manual for this machine it doesnt look hard to upgrade, but it looks to have only one ram slot. So your going to have to get a 8gb or 16gb module.
I recommend you use zram instead of normal swap, obviously more real ram is better but zram holds up really good if you only have 4gb of ram. I also have 4gb of ram and a HDD, I have tried manjaro kde/gnome/xfce and all have been very useable… with the right tweaks. Unfortunately most those tweaks are kind of advanced (changing to zen kernel, reducing swapiness) the one thing I can recommend is you to use psd (profile sync daemon) and dont open more than 4 firefox tabs.
What else would I be comparing it with when posting to someone who has 4gb of total ram? I also notice you left off the end of my comment. Thats not fair or right.
No reason to complicate anything or try to work around this issue. Just increase the RAM to 8GB (or 16 if applicable), and you’ll liberate your system from the bottlenecks you’re facing.
The first two posts already gave you the best approach to this issue.