So 4 GB is just on the edge at building time, if we suppose that last screenshot tells the most stressful moment.
And that is another thing I can’t understand: why others hit low memory and I, who uses a lot plugins and components, had zero issues 
what makes that difference?
And I used had because nowadays I have 8 GB because of AI (and for me the price difference was not so important, but that is another story).
Should this thread move somewhere else or are we seeing this as an explain why using swap helped?
Anyway. For other beginners this one example where is talked little bit about low memory and reasons for that:
That is strongly FAQ question when upgraiding fails. But reason for that is rarely explained.