Monoliths don´t scale, at least according to the microservice community. But they also claim that a duel between Godzilla and King-Kong would be won by microservices. So we will have to ask ourselves, if that is true. Scaling can mean increasing CPU and memory (vertical scaling), but that does have only limited potential. The interesting question is, if it is possible to horizontally scale a monolith, which means if we could add instances of a monolith in parallel, and increase it´s load bearing capacity by that. There are usually 2 factors that limit scalability of a monolith. The first one is application state. But some technologies offer the possibility to replicate it between the instances, and if not you can still move it to the client (like the browser) or to the database of the monolith. Which then makes the database the only limiting factor of horizontal scalability that is left.
If you manage to seperate the data that needs writing atomic transactions in your database somehow, you can actually achieve horizontal scaling as well. Just as the runtime instances of the monolith you could also separate the data into different shards of the database underneath. This is also possible with an RDBMS like MySQL (yes, the boring old technology). Every DB instance bears customers within a certain immutable hash key range. The DB instances replicate the data between them for reading purposes:
Every instance of the monolith would have one of the DB switches as proxies, so this will not become a single point of failure. If it seems hard to find the boundaries to separate the wrting transactions at first you can use the patterns of eventual consistency even for your monolith, and off you go!
This does even have a huge advantage over a microservice architecture: If it is not just one of the features that needs to endure a higher user load, but all of the functionality, than it will be a lot more effort in a microservice architecture to achieve higher scalability. This is why I do not see an advantage for microservice architectures here, and I would call this a draw.