Naruto never actually gets an '11 tails' in the series—that’s one of those wild fan theories or misconceptions that pops up sometimes! The tailed beasts in 'Naruto' cap out at nine, with Kurama being the Nine-Tails. Naruto himself only ever hosts Kurama, though he does eventually gain access to chakra from the other tailed beasts during the Fourth Great Ninja War arc. That might be where the confusion comes from, since he temporarily uses their combined power without actually 'having' their tails.
Now, if you're thinking of a specific moment where Naruto’s power feels next-level, it’s probably around episode 329 ('Two-Man Team') or 330 ('The One Who Will Inherit'). That’s when he teams up with Kurama fully and taps into the chakra of all the tailed beasts, unleashing that insane glowing red-and-black mode. The animation in those episodes is chef’s kiss—especially when he starts throwing around massive Tailed Beast Balls. But yeah, no 11 tails, just Naruto being his usual overpowered self with some extra help from his furry friends.