I read some guide posts about custodial vs. non-custodial wallets but only a few about open vs. closed source. I often read them brought up by other users in the comments. I think many beginners don't have the slightest idea about the difference between closed and open source yet. I don't claim to be an expert on this but I will try to highlight that in this post based on what I understand so far.
I was advocating open source wallets for years and people told me several times that I am to extreme with this approach, but look what is happening with closed source wallets.
They get hacked, infected by malware all the time and who knows what else is happening below the hood, since nobody can check the code.
There is a high chance closed source hardware wallets have some hidden code or backdoor that can remain dormant for years and just waits to be activated.
Few more good examples of less known non-custodial open source wallets are Sparrow wallet, Airgap wallet, Unstoppable wallet, etc.