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?