Another thing is that people sometimes will get mixed up with exchanges versus holding their own bitcoin, so if you keep your coins on exchanges, there are some risks with that, yet personally, I am o.k. with beginners keeping coins on exchanges until they start to get to higher numbers, such as $500, $1k or even more, and then once you get to those higher amounts, then you should be figuring out ways to move some or all of the BTC that you have on exchanges to private wallets. In recent times, it can be expensive to move a bunch of small BTC transactions.
I agree, anyone who is buying Bitcoin on a small scale should kept their BTC in the exchange itself because withdrawal fees are insane due to market congestion which is an ongoing issue since Nov so obviously the withdrawal fee on most exchanges are around $40 so I wouldn't withdraw unless I have around $500 or let's say once in a couple of months for someone who is been investing using DCA every week.
Withdrawing via LN is an option but definitely I won't recommend it for a beginner because they could mess up with opening LN channel and lose their BTC, so the good choice is keeping funds in exchanges but not for too long as well.
Most of them have definitely bought small-scale BTC from the exchange because a few weeks ago it became a bottleneck because the network was congested and then the fees were quite high this certainly burdened those who wanted to withdraw BTC from DCA but were constrained but now it seems that the mempool has returned to normal the fees are not so big, now the Binance exchange only charges a withdrawal fee of 0.00029 about $13 now I have withdrawn $200 of DCA results and kept some time on the exchange, so it's better to sacrifice a little with $13 than to have such a worrying risk of keeping too long on the exchange.
Make sure you have withdrawn to a non-custodial wallet and resume the DCA once it is above $200 or $500 immediately withdraw, that's what I do.
The Lightning Network is indeed a solution but for now it is still not right, it is still not popular with middle to lower investors, I also see that large investors store their BTC onchain not on LN, so make sure you stay onchain if you still don't understand the lightning network.