Thank you @mawa for your kind words.
OK, I remade the lightmap with better quality and put the " myLightmapTexture.isRGBD = true" line.
So, with a tonemapping set to “Standard” it looks like this:
And here with “ACES”:
It looks darker with ACES, I like Standard more.
It’s a pitty we don’t have access to any other tonemapping tools, like softclip or toe controls though.