Now that I have said goodbye to the Raspberry pi 400 and no longer have to deal with its limitations, new possibilities open up for Olla. The first thing I did was choose Atom to replace both Geany and Epiphany.
There's nothing wrong with the Geany-Epiphany combo, but in fact before my Raspberry pi adventure, I had already been trying Atom combined with CopyQ. I had more or less forgotten just how well Atom + CopyQ worked. I installed auto-save and html-preview in Atom. The auto-save works instantly after an edit and the preview is also refreshed without any delay. Geany needed 5 seconds before auto-saving and Epiphany also took a couple more seconds before refreshing. Not really a problem for me, but now in Atom it feels like I've replaced a donkey with a full-blood race horse...
Another very appealing fact is that Atom supports the two other Featherweb candidates: Emmet and Markdown. I have some Emmet experience with Atom, no Atom Markdown experience yet. Anyway, I hope you'll forgive my slight preference for Olla...🌝
One thing I would like to solve: each time there's a save action plus preview refresh, the preview scrolls back to the top of the document. (This was also the case in Geany-Epiphany) If someone reading this, knows the solution, I'm all ears!
[EDIT: found the answer! In Packages under atom-html-preview, just tick the box "Scroll To Cursor". Problem solved! ]