Right now: yes
There is a transitional periodtransitional period until 31 December 2020 where EU law applicable to the UK is still considered part ofcontinues to apply as if the EU for this purposeUK were still a member even though they aren’t. After that, no but presumably SO will have modified their TOS. That’s what the transition is for.
Further, any contract must be interpreted in light of what a reasonable person in the parties positions would understand. It’s reasonable to assume that this clause is there to comply with some unnamed EU law. EU law still applies in the UK so it’s reasonable to assume that it’s meant to apply to users in the UK.