With sequential Ids you use one of two sequences,

- table-global sequence :: Which leaks activity signals to all users that can create and see new Ids. This is the naive sequence you get when creating an incremental Id in a table.

- user-local sequence :: How many invoices a single user has, which is safe if kept within the reach of a single user. The sequence though, is slower and more awkward to generate.

Say you have a store that allows a user to check out just their own invoices.

- store.com/profile/invoices/{sequence_id}/

This does not imply that using a random id will return you back the data from another user, so it isn't necessarily as unsafe as you guessed. You'll probably get a 404 that does not even acknowledges the existence of said Id (but may be suspect to timing attacks to guess if it exists).

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With timed Ids you do need a data leak out of bubble of a single user. Database design should always try to guard against that anyway. That's why we salt our passwords and store only their digest (right?).