1. You're building a product that touches multiple deep domains and the business has modelled a very aggressive headcount growth
That feels like premature optimization; split when you need to and not before
2. You've outsourced a large portion of your development to a number of agencies
Then your developer count is likely not in the 10s (you need to could the agency developers), plus if you've already outsourced your development in that manner, it suggests you already chose a micro-services architecture and tendered accordingly, this feels like a post hoc justification.
3. You have a team of individuals who know nothing but microservices
If a team can build a set of microservices, they can build a monolith, the skill sets are not that different, a microservice is after all just a really small monolith.
4. Your chief compliance officer is intimately familiar with the data protection benefits that microservices bring and is leaning heavily into it in their regulatory submissions as a way to compensate for some other gap in the business
That's an interesting one, you're trading technical complexity for compliance, and it may well be a use case, there is not enough data to comment here. But there are many ways to be compliant with , micro-services might be one, but is it the optimal solution for all involved, well that depends...
5. You're building anything to do with image processing at scale
This doesn't require micro-services, it probably requires horizontal scalability, if its offline processing you might want a batch process you can turn on and off as required, but that doesn't have to mean microservices, at this point it becomes a semantic argument of what constitutes a microservice, but I would argue the idea of batch processes predates the idea of microservices. Also just because you might need to use microservices in a small part of your application stack, the rest of the solution can still be a monolith: a hybrid architecture if you will.
6. You are a subsidiary owned by a parent company with tons of experience and tooling for microservices
Again, if you have tons of experience with microservices that can be easily translated to monoliths, just build a microservice but bigger
7. One of your VCs has offered up a dev team they own to speedboat your MVP, who specialize in microservices
It its 10 devs or less, does it matter, build a monolith and optimize when it makes sense to do so
8. You've received a buyout offer by a party interested in specific IP within your product, with the condition that the IP is isolated from other parts of the system
Unless that is your goal from day 0, I'm not sure how you could anticipate this, again this feels like a post hoc justification. If, in the unlikely event that that situation occurs, that might be a good time to consider splitting out that functionality.