UK airports were always doomed to be very quiet anyway through W20/21. C-19 will continue to be a scourge, as vaccination programmes won't have time to take effect until well into 2021. Many countries will insist on either a clear covid-free test taken within 72 hours before departure, or (later) evidence of innoculation. Others will continue to impose quarantine requirements upon all arriving passengers. The UK itself isn't exactly rolling out the welcome mat at the moment either.
No doubt there are media elements who wish to cast Brexit in the worst possible light for political reasons, but the reality is no change. UK visitors remain excluded from some EU countries now (eg. Eire, unless self-isolating for 14 days). Others will welcome UK tourists to support their essential hospitality industries. Major markets will not be excluding UK travellers on the grounds of Brexit. Covid is another matter, but infection rates will drive decisions on that.
Note also that there may yet be a 'deal' anyway. All negotiations with the EU on any issue always go down to the wire, with all parties claiming they are miles apart with just hours to go. There are lots of precedents for this. Its the way they do things, and political pantomime was always bound to be part of the game on something as high profile as Brexit. Neither side can afford to be adjudged as having caved-in easily. Though if there is no trade agreement, I'm fine with that based on the terms being offered at the moment.