What you can be sure of is, after 1 January 2021, we are likely to get shunted into the non-EU queues at many airports. That *will* be Brexit!
We are no longer in the EU. We therefore no longer have any of the privileges that EU members do.
Right now, the transition period is insulating us from that reality, like a dam holding back a wall of sewage.
1 January 2021, the dam bursts.