I feel like some tricolours should get a pass. France and the Netherlands are the OGs, but many others are great too! Estonia’s is my favourite colour combination, but Germany, Lithuania, Romania, and Bulgaria are pretty recognisable too. Sierra Leone and Gabon have pretty underrated tricolours too. There are some that are too similar to others, like those of Russia (very similar to the Dutch), Chad (nearly identical to Romania), and Italy (pretty close to France, in my opinion Mexico did the colour combo better with the cool eagle)

As for the bicolours, you have the triage of Poland, Monaco, and Indonesia who are really similar. Poland should add their eagle back to the flag, birds are cool and it’s deeply tied to their history, and Indonesia needs to spice their flag up to be more interesting. Monaco should probably be annexed into France, maybe they could be an autonomous province or something. Then you have Ukraine, who have a pretty neat flag that is easily recognisable, but yes it is a little boring.

Austria and Latvia are quite similar to each other too, the latter has a thinner strip that’s more unique, but I feel like both could be improved.