Every year The Economist publishes the "Democracy Index," scoring countries from 0 to 10 based on five criteria (electoral process & pluralism, functioning of government, political participation, political culture, and civil liberties). The most recent report is for 2019, and includes scores for 167 countries. Norway scores the highest at 9.87, and North Korea is last at 1.08. 22 countries scored above 8 and so were considered "Full democracies."
The 4 categories are:
Full democracies (8-10]; 22 countries in 2019
Flawed democracies (6-8]; 54 countries in 2019
Hybrid regimes (4-6]; 37 countries in 2019
Authoritarian regimes ([0-4]; 54 countries in 2019
How many countries will be considered "full democracies" (score higher than 8) by The Economist in 2021?
This prediction resolves as the number of countries (or other polities) being categorized by The Economist as "Full democracies" for its report covering 2021. (I expect this to be published sometime in the early 2022.) Note that not everything that gets a score is a full-fledged sovereign state. Data can be found at the Economist Intelligence Unit's website (here's 2019, probably gated) and at Wikipedia.