Would the Subtle Spell metamagic or the Aberrant Mind sorcerer's Psionic Sorcery feature let you cast spells while using a shield without proficiency?

Question

The PHB's rule on armor proficiency states that you cannot cast a spell while wearing/using armor you are not proficient with.

The Metamagic option Subtle Spell lets you cast a spell without having to perform verbal or somatic components. Alternately, the Aberrant Mind sorcerer's Psionic Sorcery feature takes away the need for V/S/M components entirely if you cast one of your Psionic Spells by spending sorcery points (TCoE, p. 66-68).

Say you are wielding a shield, but you don't have proficiency with shields.
If you use Subtle Spell or Psionic Sorcery to remove the need for spellcasting components, would it overrule your lack of shield proficiency and allow you to cast a spell?

Answer 1

No, as these features make no mention of changing the proficiency requirement.

5th Edition uses a “specific beats general” rule. Here’s an excerpt from the rule as summarized in Xanathar’s Guide to Everything (p. 5):

[...] a general rule is in effect as long as something in the game doesn’t explicitly say otherwise.

This means that for a rule to create an exception to another rule, it must do so explicitly.

Since Subtle Spell and Aberrant Psionics make no mention of shield and armor proficiencies at all, they do not interact with them in any way. Therefore, to cast spells while wearing armor or a shield, you must be proficient, even with Subtle Spell or Aberrant Psionics.

Answer 2

Equipping armor without proficiency prevents spellcasting, regardless of components

The rule for casting in armor says (PHB, p. 201):

Because of the mental focus and precise gestures required for spellcasting, you must be proficient with the armor you are wearing to cast a spell. You are otherwise too distracted and physically hampered by your armor for spellcasting.

Note that spell components are never mentioned. Wearing armor you aren't proficient with disrupts your ability to cast spells, regardless of whether that casting involves any components or not. As a lore justification for this, the rule says that in addition to being "physically hampered" (i.e. disrupting spell components), it also makes you too distracted to maintain the required "mental focus" to cast a spell. This applies equally to subtle spells as well as psionic spellcasting, along with any other kind of casting that eschews spell components. In fact, this even applies to spells cast from items, which generally don't require components. I'm not aware of any way of casting spells that overrides this limitation.