They are vulnerable to mortal workings. That's the reason iron and steel are extra-fatal to them. Even so far as paralyzing them when immortal fae are penetrated by it. Way back in Death Masks (?) Harry dumped reality powder of Lea, which was mostly made of depleted uranium powder, and it burned the crap out of her.

The reason why Molly can use high tech is that the mantle has either suspended her mortal magic, transformed it into fae magic, or somehow overriden her Murphyonic field. There is precedent. Harry and Molly used to sit inside a circle to have their magic contained if they wanted to watch a movie with their friends or family. Perhaps the mantle does the same thing, traps her magic inside her body somehow and applies a skin of the mantle's magic over her.

Equal exchange is part of balancing the scales. E.G. Butters removing the rebar from Mab's neck during the Battle of Chicago. He was not bound to do so by contract or treaty. Once she was back on her feet she offered him a favor to balance their scales. Even when Harry, as the Warden of Demonreach, bound Ethniu, he was then able to bind Lady Molly to pay for all the medical aid and funeral for Chicago. Because the Warden is not bound to Winter or a signatory of the Accords. By binding Ethniu, he put Winter in his debt. Ethniu was Winter and Accorded nation's enemy. Winter had to balance the scales with the Warden.

Mab passing through Harry's threshold was a matter of guest rite. Since she was not offering him any harm, she was behaving within guest rite and allowed to enter without permission. Though, as we saw in The Law from Harry's perspective, most of her power was probably left outside.

The Svartalves made Harry's upgraded ring in his workshop. Which was copper, silver and iron, combined into one ring. He had to pay a premium for them to work with iron. I thought he'd lost it in Changes, but it was still there in PT. But, per WOJ, not everything native to the Never Never is vulnerable to iron. (At least not vulnerable beyond the usual, like being cut by a steel sword)

The obligation against lying is Winter Law not particular to the Mantle, so Nemesis suborned Winter Law, breaking the restrictions of the Mantle would have meant Maeve becoming a undifferentiated lump of protoplasm. The same happened with the Mantleless Lea.

This fits in with my theory that Nameless became subject to Winter Law solely in order to destroy it, (he is a Demi-god of Discord, and a crooked Lawyer) his aiding Nemesis just one of the aspects of his attack. Without Winter Law then Winter would lose its coordination, massively undermining the defence of the Gates. Oh and Nameless is Cowl of course.

Slight correction. The prohibition against lying, or, more correctly, the requirement to tell the truth at all times is a fae requirement. Like the vulnerability to cold iron, all fae have this. Not just those under Winter Law or those that are part of Accorded nations.

It's a mortal cell phone. In SG she walks away and Harry sees her use it. In PT he summons her and she's using a cell phone that the mortal summoning magic lets the magic smoke out of.

Molly also thinks she can leave the circle, but when she presses a finger to it, the fingertip deforms like she's pressing it against glass.

Mab's instruction to Harry was to "Kill Molly Carpenter". Not, kill lady Molly. Or kill the Winter Lady.
Names, offices and mantles are incredibly important to the fae. Mab summoned Kringle, not Vadderung. Same person, two different names and offices. Harry bound Molly because the Warden of Demonreach did a favor for Winter, by enforcing the Accords and binding Ethniu. Winter was obligated to repay the favor and he called upon them to pay for the funerals and medical bills.
Harry Dresden, The Za Lord, The Wizard of Chicago, or the Winter Knight could not have bound Ethniu. Only the Warden of Demonreach could have bound her.
Name and mantles, kid. That's how they get you.

Harry cut off all other prisoners not in the same confinement mode from communicating with Thomas. There's only one prisoner before Thomas in 'contemplation' mode. The British guy.

I'll be quite honest, I'ma lose my cool with you real quick. The books entirely support that position, they DO NOT support your position.

I'll break it down for you, Barney-style.

The fae lady mantles are supposed to go to the closest reflection of their court.

Lily was an undeclared changeling. Her mother was a Nixie, making her a mortal, technically. But Nixies are members of the Winter court. FLAW.

Lily said that no mortal has ever been given a fae queen mantle.

Mab confided in Harry that she was once mortal. FLAW. It's a double FLAW, since Mab and Titania are twin sisters per WOJ. Whoops! It's a quadruple FLAW, since Maeve and Sarissa were Mab's twin daughters by an Austrian composer in the 19th century, and Maeve was already the Winter Lady.

WOJ is that a person possessing a fae mantle can't acquire another one, since they would be 'full'. https://wordof.jim-butcher.com/index.php/word-of-jim-woj-compilation/woj-on-the-fae/ On this page, all the way at the bottom.

Lily was the Summer Knight and acquired the Summer Lady mantle. FLAW.

In Summer Knight, Aurora just dies. Harry doesn't even find out until days later that Lily is now the Summer lady and Fix took up the Summer Knight.

In Cold Days there's a big dramatic sequence where the mantle coalesces into a big green bird-like figure and leaps from Lily's prostrate form into Sarissa. The same thing happens between Maeve and Molly, only the bird is blue. FLAW.

These are contradictions. We are being told one thing and being shown another. Until an errata sheet is published, there's no clarity. And, FWIW, Jim has said out front, that he WILL lie to us. Until and unless it's shown and explained in the books, it's not written in stone. And even then, comic book rules apply. Harry is a rule-breaker. See also: Law of Magic 1 and 5.

Just my take on it, but Molly's soul is not currently in jeopardy. The fae courts had to have been set up with TWG's approval. It's the only scenario that fits with TWG kicking out all the small G gods or making them surrender their immortality to continue to interact with humans.

If the courts were set up with TWG's approval, then TWG had to know what it would do to the mantle wearers. And how their choices would shape their destinies. And that making those choices, gaining power, and losing free will, would cost them personally.

I mean, it's not like TWG isn't all about sacrifice on behalf of others.

Mab was just twisting Harry and trying to make him doubt his course of action. It's her way of trying to exert control over him. And that's a losing gamble, no matter who you are.