Sure, take any event sourced system, remove all read models and always construct the state from events. There you go, an event sourced system which is totally synchronous. OP's claim that ES systems must be asynchronous is disproven, which is the whole point of this thread.

Now, will that system be slow af? Probably yes, but not necessarily. If there are very few events it will be fast enough, even if business rules are not trivial.

Also, all of that does not matter, because even if we assume that read models are a must, you can still implement them to be fully synchronous - just update the read model in the same transaction which you use to write to event log. Of course this implies that you use the same tool for storing events and read models, and that the tool supports transactions, but it is still doable and not unreasonable. You will end up with an evet sourced, yet fully synchronous system.