Where did I say that this forum is the only place to learn about bitcoin, bitcoin wallets and cryptocurrencies? It should not be hard for you to understand what I mean. What I meant was that the chance that people will know about opened source and close source wallets is high on this forum. Despite that I know what self-custody wallets are before I registered on this forum, I did not know what open and close source wallets are. This forum expose us to many information that we might not find out on our own.
That's the nature of the forum; even in other forums, not everyone has skills in deep research. I know it's hard to find some resource and knowledge by just using the google search engine. Unlike here on the forum, you can make a thread and ask everyone what is this and that are.
That's the purpose of the forum: to discuss something that we don't know or to contribute to the community.
About the wallet, custodial or non-custodial (self-custody), if this is just what you know, not all self-custody wallets are open-sourced. That is why someone here is pointing to an open-source wallet.
One of the non-custodial, or self-custody, wallets is Exodus Wallet, which is closed source; it is not a recommended wallet or a hardware wallet like Ledger Nano.
How can you make sure they don't add something to their wallet even if they say we have full control? Do you think you are safe with these wallets if you don't know and verify the open source?
Having self-custody wallet isn't enough; you still need to know what it means to have self-custody it's either open/closed source.