You don't even need to know about self custody wallets or even have access to one before you can start investing in bitcoin as a newbie, you will find that alot of bitcoin investors started holding with one exchange or the other before moving on the custodial wallets and today are still holding and accumulating more bitcoin, it's not a must that you must start with a self custodial wallets as a newbie before you can have any chance of success in bitcoin investment, what's most important for a newbie to know is that they need to invest with their discretionary income using a strategy that won't put too much pressure on them and the DCA is that strategy, common sense can help lead them through the rest.
Everyone must not start the same way and now is the era of information wjere everything is at your finger tips, so you are not entirely correct on this, a newbie can start holding his first Bitcoin from a private wallet and not in centralized exchange. There have been many reports of exchange collapse and scamming centralized platforms that people can easily learn from to be safe. Besides, some newbies joined Bitcoin through recommendation of friends so they will definitely start very well and with the right information.
I don't want to believe that you are omg those who think that self custody is something reserved for only experienced investors, even beginners can imbibe that habit and they will hardly experience scam or loss of funds which is a big motivation for them.
A beginner must not know all these before starting out, it's not a priority. This can be learned as he keeps buying and holding. The most important thing is to get started, even if he starts holding on an exchange. As times goes on he continues learning and patronizing better knowledge and of course starts appreciating self-custody, he would know the best non-custodial wallet to use for self preservation of his coins and then he would transfer it from the exchange to the correct non-custodial wallet. Sending coins to the wallet Everytime he buys might even be very expensive for the newbie if the fees are high and can be discouraging, so it's even better he holds on the exchange for a while and learns how to consolidate his coins there for a while before sending to his wallet to minimize fees.
Stop placing so much requirement on the new investor, he only needs to start as long as he has discretionary income and knows how to buy, he can learn more as he advances in his accumulation journey, he has time to learn that, learning is a gradual process and as he remains committed to his investment journey, he would learn other good practices as regarding safeguarding his sats as he progresses.