Since Milo is, in fact, the first Pokemon Gym Leader you will face in Pokemon Sword & Shield, he makes for a pretty easy defeat. This has usually been the case for first Gym Leaders in Mainstream Pokemon Games, and Milo is no different. If you select Scorbunny as your Starter Pokemon, Milo is all the easier to handle since his Pokemon are extremely weak to Fire Type Attacks.
However, even if you don't select Scorbunny to journey through The Galar Region with, Milo can still be handled if you make the correct choices leading up to his Pokemon Gym. One thing you can do in this case is capture Rookidee in any of the routes prior to arriving in Turffield. Wild Rookidee almost always have the Flying Type Attack called Peck, which will do loads of damage to Milo's Grass Type Pokemon. Rookidee can also learn the Flying Type Attack called Pluck at Level 16.
But should you not want to start with Scorbunny or capture Rookidee in preparations to facing Milo, you don't actually have to in order to defeat him. Milo's two Pokemon will be at Level 19 and Level 20, respectively, so one could, honestly, train all of their Pokemon to Level 25 or Level 30 and still easily defeat Milo. This is incredibly simple to do if you participate in plenty of Max Raid Battles in the Wild Area and stock up on EXP Candy.
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