Why Manjaro freezes?

I’ve been using manjaro for about a year. Before that everything was fine, but after the last major update, Linux started to hang twice a day. Nothing helps, I just have to reboot. Where to look at all, what can be the reason?

I use Intel GPU (free driver)

It is impossible to have an opinion on. You will have to read your log files and you will have to be a lot more specific. Please read this on the wiki Forum Rules - Manjaro and this topic on How to provide good information - then post the info relevant to your issue(s)

I have been using Manjaro exclusively for the past 4+ years (almost exclusively on Intel) and my overall experience super positive.

But as you mention KDE I am completely at loss but I can say - the shared components - the core Linux system which every edition build upon - is rock-solid.

KDE is almost always a work-in-progress and - more often than not - this introduces regressions and unwanted behavior.

Have you tried other kernels?