Lightweight synthetic high loft skirt?

Rab makes one.
It’s currently on offer at Sportpursuit, if you’re happy to buy from the UK (you might need to be signed up to follow the link).

Some skirt links. No experience with any of these:

Ultralight Apex Insulated Skirt, Waist Wrap – Etsy
https://www.etsy.com/listing/1741497795/ultralight-apex-insulated-skirt-waist?click_key=76f396c17c0f8c9f261d98b2312495de9ccfddd2%3A1741497795&click_sum=c2b81c61&ref=shop_home_recs_1&cns=1

MontBell Thermawrap Skirt
https://www.montbell.com/jp/en/products/list?q=thermawrap+skirt

Rab Cirrus
https://rab.equipment/us/womens-cirrus-insulated-skirt

Functional Clothing Lab
https://www.instagram.com/functional_clothing_lab/

Skhoop of Scandinavia The Original Insulated Skirt
https://www.skhoop.us/

LightHeart Gear (LHG) hiking skirts and dresses
https://lightheartgear.com/products/fleece-skirt-1
https://lightheartgear.com/products/fleece-dress#

Winter Layering Staples! Alpa Direct with Wool Jacket & APEX Quilted Skirt : myog
https://www.reddit.com/r/myog/comments/zstfou/winter_layering_staples_alpa_direct_with_wool/?share_id=qzI5ieOePQTWJa7J1rdnQ&utm_name=ioscss

Equestrian Riding Skirt for Women Winter Riding Gear – Etsy
https://www.etsy.com/listing/668938645/equestrian-riding-skirt-for-women-winter

Insulated “skirt” : myog
https://www.reddit.com/r/myog/comments/1aunxqo/insulated_skirt/

The Wearable Blanket – NorSari
https://norsari.com/

Purple Rain Adventure Skirts-Shop-Ultralight hiking kilt
https://www.purplerainskirts.com/shop/adventure-kilt-black

Macabi Skirt – Light Gray – Macabi Skirts
https://www.macabiskirt.com/products/original-macabi-skirt-light-gray?variant=40838087803063

The Rab was the best one I saw until now, but still well over 200 grams.

I found an old article from Blister listing several, and it had a lightweight option from Shkoop, but all the current ones I saw were over 300 grams.

Montbell doesn’t have a zipper, which seems like itwould be a lot colder, and still not very light.

I will check out the ones you folks  linked that I had not seen yet.

Most of these are pretty simple: shell fabric, insulation, fittings (zippers, cinches, etc). Lighter weight will necessarily be less warm, less rugged, fewer features, and/or smaller. Same as choosing an Apex jacket.

I would think that the small shops can probably make exactly the warmth and weight that you want, including a Torrid clone (LHG, Etsy, Functional Clothing Lab, seamstress).

You could check out the Skhoop insulated skirts—they’re lightweight, packable, and come in a few different styles. Another option might be Patagonia, as they sometimes have insulated skirts in their winter gear lineup. If weight is a big concern, you might also look into DIY options using ultralight materials like down or synthetic fill.