all European clients receive this protection as it applies to the accounts themselves which are open to being made by non-uk residents. in this case, Interactive brokers and Barclays are both UK registered and fall under this scheme.
whats worth noting is that the protection means if your account is larger than £85000, you are protected to at least £85000 and will receive more than this in reality. you may not get everything back, but in the worst case scenario you still have £85000 and in the more likely scenarios you will get back more.
the £85000 is a protection applied in the case that a default happens, which is extremely remote for those who meet the necessary fund reserves. Trading 212 meets these reserves and so you wont need to worry about the protection amount, your funds are secure.