Even though self-custodial is important, you do not need to learn self-custody before getting started investing in bitcoin. In investing in bitcoin, amongst the most important of things is to get started, as long as you have a discretionary income.. start right away, and if you don't know things, then just start out smaller and learn as you go... so for example, if you know that you have $100 per week that you could put into bitcoin, you might start with $10 per week and work your way up to $100 per week as you learn various basic aspects of bitcoin. Each person will be different in terms of how much time he has to learn and at what kind of time line does he need to figure out some kind of a self-custody solution, whether electrum or some hardware wallet or some combination, and of course, there can be needs for timing, but there are likely greater needs to get started buying some bitcoin first.
Of course I would agree with you that it's not much of the basics to invest in bitcoin but it comes along the line of accumulation and fortunately coin security is my most priority I encourage people to start making all type of coin security decisions before or once their accumulation is up to $500 or even below since exchanges pose more risk. Cold wallets on airgapped device is most important for a holder even some are not willing to go for a well secured wallets like electrum yet they can go for any other open source wallets that at least has no backdoors like exchanges and other types of wallets.