Can Apple / Google modify my apps?

Do Apple / Google have a technical capability to modify apps without developer knowing?

I'm writing article about implications of using app stores for distributing Web3 apps.

Particularly I'm curious if they can potentially modify apps and introduce surveillance features. For example, if the government compels them to extract someone personal keys from Web3 wallet.

For clarity, I'm not asking if they are doing this actively. I'm curious if this is technically possible.