24 nations qualified for Euro 2020 and according to whose list you consider as accurate, there are between 44 (United Nations figure) and 51 (Wikipedia) countries in Europe.
Here are three more that didn’t make it to the finals.
Iceland

The tiny nation of less than 5 million people qualified last time and actually knocked out England.
I visited in January 2015 for a milestone birthday and was stunned by the beauty of the country. No whales or Northern Lights made an appearance, but not to worry!
Þingvellir National Park, Iceland Gullfoss, Iceland Skollfoss Geysir, Iceland
Romania

I have been to Romania three times, first time to ski in Brasov, and then on Eastern European train tours (Budapest to Bucharest and Belgrade to Timisoara).
The building pictured above is also known as Ceaușescu’s folly. The generally despised former dictator wanted a symbol of Romania’s greatness so commissioned the mammoth palace that is the world’s second biggest municipal building after the Pentagon.
I loved Timisoara. Some of the most impressive squares in Europe and a wonderful cafe culture. I must return one day.
Timișoara, Romania Unirii Square, Timișoara, Romania Unirii Square, Timișoara, Romania West City Radio Building, Timișoara, Romania Libertăţii Square Tram Timișoara, Romania Serbian Orthodox Bishop Residence, Timișoara, Romania
Albania

I have ventured to the former reclusive nation twice and loved it both times. The decade between visits saw much change – not all of it positive.
In 2007 we did two very enjoyable if extremely slow train journeys (average speed 30km/h), but ten years later the country had no trains at all.

It may surprise you that Albania has some lovely coastline, extensive Roman ruins and plenty of tourist worthy sites. I show a selection below.
Skanderbeg Square, Tirana, Albania in 2017 Bric A Brac Stall With A View, Sarande, Albania Sarande Blue Eye in Southern Albania Ionian Sea View From Hotel Titania Breakfast Terrace, Sarande, Albania Skanderbeg Square, Tirana, Albania In 2007 – View From The Museum Lake Butrint, Albania Millinery Shop Albanian Style, Sarande Sarande, Albania