It’s a pity that we can’t enable the shopping cart for just some events.
For ongoing repeated events during the year, we really need the shopping cart.
For a big once-a-year event we need ticket types, but the shopping cart breaks ticket types (they are not recorded). The cart also does not work at all with ticket types on the frontend.
Unfortunately, you cannot have both for this case. If you want to use Ticket Types with shopping cart, all of your events will need to have ticket types defined
For your case, some events have ticket types, some don't, so it won't work. You cannot use shopping cart for this case