People have made money on the Internet for decades before Substack. Ask your customers to mail you a cheque, or send them a Paypal/Venmo/Cashapp payment and manually process their subscription. People will understand that you're not Amazon and waiting a day or two to get access to your content won't be a dealbreaker for them. This way, you control the pricing and spare your customer the hassle of another monthly subscription.

If your newsletter is a side gig, sure, use Substack. But if it's your primary source of income, it's bad business to be subject to the whims of a platform you have no control over. Worse still when it's not a self-sustaining business whose primary obligations are to venture capitalist growthbros rather than paying customers.