I have a Dropbox Professional account, which is listed on the Dropbox pricing plan page a "Business" account, however, when you then look at your login page, it lists it as a "Personal" account.
On the Dropbox GDPR compliance page it states: "If you are a Dropbox Business customer, please note that you are the data controller, and have specific legal obligations under the GDPR. Dropbox acts as your data processor in these cases. "
It also states: "If you are a Dropbox Basic, Plus or Professional user, Dropbox is the data controller of your data. Please also note that there are specific legal obligations in that regard under GDPR."
So basically, it's my understanding that a Professional account, whilst being listed as "Business", is actually not a business account, and thus does not fulfil a businesses requirements under GDPR as Dropbox will be considered the Data Controller, and as a Data Processor, I don't have the permission to hand over Control of my data to another person.
So the only option I have with Dropbox is to sign up for a Business Advanced account which requires a three user minimum subscription, or £540+VAT per annum.
I'm using Dropbox in the UK without issue - you simply need to document the data flows and ensure it is going to a place where it is stored appropriately (i.e. it isnt to a server is sombody's back garden!). You also need to document it and ensure that its recorded in your policies etc.