You’re correct!!
I rebooted my ubuntu server, which allowed me to have around 7 to 800 MBs of free ram on my instance and bootstrapping succeeded. I’d have stop my container before another BS, if another rebuild/bs didn’t succeed after enabling the desired plugins.
But I’m astonished at the new ram demands of the discourse. As the cost of the instance/droplet is almost doubling when I go from 4 to 8gb ram. Which I don’t wish, considering that mine is a very very very small website (perhaps 10 visitors a day). Earlier Discourse’s standard install shown to demand only 1 to 2 gb ram.
Thanks very much for helping me recognizing what was going wrong.