Where does Apple Appstore commission for inApp purchases apply? I always knew that Apple has commission from paid apps, but I only just found out this applies to inapp purchases as well. Due to this, many apps raise the price of their inapp purchases on appstore so that they do not lose revenue when compared with other platforms where they sell these services. This obviously worries me as I do not want to spend more money than I have to and I want to know, when does the commission apply so I can try to avoid it as much as I can.
Examples of this:
YouTube premium - costs 13$/month on iPhone, but 10$/month everywhere else - 30% extra
Twitch Subs - cost 6$/month on iPhone, 5$/month everywhere else - 20% extra
Spotify premium - costs 7.3€/month on iPhone, but 6€/month everywhere else - over 21% extra

I do not know any other examples than this, but I am sure there are many, because not everyone is willing to take a 30% revenue cut.
My questions are:

Does this apply on shopping apps like Aliexpress, eBay, Wish or not?
Where else does this apply?
What should I avoid paying for through an iOS app and rather pay for through my PC?

I mean I pay monthly for many things. If I slapped an extra 20% on only half of them, I would be paying quite a bit extra! Say you pay for YouTube premium, 2 Twitch Subs and a Spotify Premium, which would total to 20$ and 6€ (about 27.5$ total) per month, but through iPhone it would cost me 25$ and 7.3€ (about 34$) per month, which is almost 7 dollars per month, I mean thats almost enough for another membership somewhere.
Yes, Apple takes a cut of the price both purchasing an app itself - and for in-app purchases. If they didn't do this, I imagine all apps would be free, requiring an in-app purchases - effectively circumventing the whole system.
This is similar to how it works on Android phones, where Google Play Store takes a similar cut of both the initial app price and additional in-app purchases.
On both the Apple App Store and the Google Play Store, the standard cut is 30% of the initial app price as well as for in-app purchases. However for subscription based in-app purchases, the cut is reduced to 15% after one year.
If the seller is a small business the fee is reduced to 15%. On the Apple Store that applies for companies selling less than $1 million worth of product on the App Store in a year. On the Google Play Store that applies for the first $1 million worth of product sold in a year.
Your question is then about shopping apps. The fees above apply to everything sold through in-app purchases. Items that you purchase by other means are not affected.
This means that for example physical goods and services, and person-to-person services (for example online fitness training, online tutoring services, medical consultations, etc.) are sold by other means, thus you're not paying Apple or Google anything in that case.
For some types of apps with digital content, Apple allows app sellers to let users access content they have purchased outside the app - for example from a PC. This is typically the so called &quot;reader apps&quot; (tv/movie streaming, magazines, newspapers, e-books, music streaming, etc).
Remember that when you purchase subscription from a vendor web site instead of through the App Store, you'll have the terms and conditions given by that web site. They might be worse than what you'll get from the App Store.