"What were the lightest weight fork with relatively plush and nice suspension and excellent build quality from the late 90ies?"
Depending on your budget. If you're OK with linkage fork weirdness I would say a Mk.2 Look Fournales carbon fiber linkage fork. Around 1400 grams in a size large, 80mm travel, very plush due to full bearings on all linkages (I'm restoring one right now and there seems to be zero friction in the system with all new bearings), and very stiff. Not everybody's cup of tea as far as the design of it goes, kinda expensive too and rare.
Otherwise I would say a SID would work fine if you want a light telescopic fork (and you don't do any rough riding).