I should say that the wording of the law is straightforward: it applies to any service that “has a significant number of UK users, if the UK is a target market, or it is capable of being accessed by UK users and there is a material risk of significant harm to such users.” (And it’s their definition of risk, not ours.) (UK doc here)
What I don’t pretend to understand is the enforcement mechanism, i.e. the process by which the UK government brings us to court and fines us approximately a thousand times as much money as we have in our bank account. As Mike Russo just said, this is messy and you have to understand the legal system to talk about it.