Generally, and as noted, flair is obtained by exchanging Shinedust for an instance of flair to be applied to specific cards. Different cards also have different flair that can be applied to them depending on the Pokémon and their types, and they can be downright cheap or somewhat more pricey to obtain. For those who have lots of Shinedust to spare, they can certainly obtain whatever flair they may desire to make their cards look attractive.
Flair also has two main types: cosmetic and battle. The former type applies to the cards themselves, while the latter type applies to when they are used in battle, particularly when they are placed in specific positions over the course of a battle. Before exchanging Shinedust to obtain them, the flair is also demonstrated with the specific card a player uses to obtain the flair, so they can see how the flair looks like before they make the exchange.
Somewhat related, though not completely, is the gold frame for cards, which do appear right next to flair. In the past, these (for individual cards) were obtained by exchanging 10 duplicate cards, but now they are obtained when 10 duplicate cards are collected in any way, including card point exchanges and Wonder Picks - which seems to be a fairer trade. Though it's not flair exactly, the fact of its appearance and enhancement makes it a worthwhile mention.
TCGP could be said to be keen on the visual aspect and using it in various ways for making itself different from the regular physical (and Live) TCG, as well as emphasizing its electronic nature. The feature of "flair" makes all of that evident; it takes a little bit to understand - hopefully so with the help of some of the pointers above - but once understood, the visual appeal of this implementation can be brightly seen.
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