#Vim, (削除) 59, 57 (削除ここまで), 48 bytes/keystrokes
$:let @q=float2nr(sqrt(col('.')))."|li<C-v><cr><C-v><esc>@q"<cr>@q
Since V is backwards compatible, you can Try it online!
I randomly received an upvote on this answer, so I looked over it again. My vim-golfing skills have greatly increased over the last 7 months, so I saw that this answer was very poorly golfed. This one is much better.
DJMcMayhem
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