Well looking at the round of 16 matches, you can even doubt the possibility of Spain, Germany, and France to easily win their round of 16 matches.
Take for instance, Germany will square it up with Denmark, and Spain to face Georgia, while France to Belgium. Do you think it's an easy match not a tough match for them?
Take a look at the picture below for the round of 16 matches fixtures.
The teams you mentioned Germany, Spain and France are easier to say they will win considering the quality of the squad players is quite good so it is natural that many people say these teams will qualify easily, but this is a match that can sometimes be difficult against underdogs.
Germany vs Denmakr is likely that Germany will win but it cannot be denied that this team will lose.
Spain vs Georgia is a no-brainer, especially since Spain didn't lose in the group stage.
France vs Belgium is a bit difficult as Belgium is a strong team although they faced difficulties in the group stage but it will be an intense match.
For me the tough matches are Italy vs Switzerland and Turkey vs Austria.
On paper, Germany, Spain and France are favorite clubs considering the depth of the squad they have, but France struggle looks tougher because they have to face Belgium. Next, I personally think the favorite teams to qualify for the next round there is Italy Italy, England, the Netherlands and Portugal. As for Austria versus Türkiye, personally I'm a little undecided, but Austria seems more worthy of being the favorite. Of course, these predictions can be completely or partially wrong, but I think some predictions will go according to expectations.
It is possible that non-seeded teams will play beyond predictions, they could make a surprise, because after all their ambitions and opportunities are equally open. If you look at the course of the Euro this time, and look at the strength of the favorite teams, it looks like Italy will have difficulty retaining the trophy. We'll see how the round of 16 matches roll out, who knows, the teams that are favorites to qualify for the quarter final will be eliminated early.