I’ve used vapour barrier socks when winter climbing (Scotland and the Alps), they were made by Patagonia and the recommendation was to wear a very thin liner sock then the VBL sock then your normal thick insulation sock. Definitely worked though your feet did feel like they were sliding around inside your boots!
TBH, a plastic bag sealed at the ankle with a velcro/elasticated strap would be just as good and way cheaper.
When I was doing the Rovaniemi 150 (why I was in Lapland) I found there was a very narrow window of being comfortable and you really needed to keep on top of things according to how much effort you were expending. As an example, the checkpoint at the furthest point of the route at Kuusilampi was followed about thirty minutes of riding later by a very long, steady downhill section – it dropped about 130m in 16Km. I didn’t get wrapped up properly before this and I was well past the next checkpoint, maybe 30Km further, before I was warmed up again. Mostly it was a case of buff over/off mouth and nose or open up the front of the windshirt by a few cm, it was very small changes.
So if there was a hill ahead I’d open up the windshirt and pull down the buff as you don’t want to overheat, as I’d get to the top then the windshirt would be zipped up and if there was a descent, pull up the buff. In the instance above I probably should have put my duvet on!