I'd use a scrap piece of material and mark with same pen, try various solvents, those suggested + white spirit and methylated sprits. See which is most successful and use that on your duvet.
I would expect isopropyl alcohol to dissolve it completely, then introduce a soapy material such as washing up liquid before it dries out, followed by thorough rinsing with clean water. Isopropyl alcohol is not easily found on its own in the UK (pity) but it is a constituent in various things such as some wet wipes, hand sanitiser (Covid type), etc. (read list of ingredients to identify the right product).
Online, quite right - I was thinking of immediate access to it like at supermarkets, DIY outlets etc., nothing like as easy as say meths, white spirit, etc. Agree entirely with gingejbee, enormously handy with a multitude of household uses.