It was rumored for quite some time but today, the WBSC announced that the European Championship will expand from twelve to sixteen teams, starting with next year’s edition that will be played in Italy.

All teams that participated in the 2019 edition, will participate in the 2021 edition. This means that the two countries that were demoted to the B-group will be back in the A-group again: Croatia and Sweden.
Besides these twelve countries four will come from qualifiers that will be played in Moscow (Russia), Utena (Lithuania), Beograd (Serbia), and Bratislava (Slovakia) in a time frame between June and July.
Countries that will participate in these four qualifiers will be those countries that participated in the 2019 European B Championship for sure: Switzerland, Lithuania, Slovakia, Belarus, Poland, Finland, Russia, Greece, Serbia, and Ireland. It is not sure if Romania and Bulgaria, who finished last in their B-Group championship groups will be allowed to participate. But likely the last two countries will be added to make a nice group of twelve countries, that is easier to divide over four tournaments.
The winner of each qualifier will head to the main tournament in Italy.