AutoHotkey (v2), 70 bytes

a:=(r:=(n)=>n?"a" r(n-1):"")(A_Args[1])
MsgBox a ":=0,MsgBox('" a "')"

Output when arg is 15:

aaaaaaaaaaaaaaa:=0,MsgBox('aaaaaaaaaaaaaaa')

Port of Sisyphus's answer

><> (Fish), 72 bytes

'.07{o}-1;!?:+0'i::9)$f)+1+0$.
v'0'
v'W'
+f-$~'f'$f1+0.
>'g00r"'l?!;o74.

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First challenge answer!

Might not be the absolute most optimised, but I couldn't find any way to optimise it more. I'm assuming this question is still open to new answers, but tell me if that is wrong.

Output when the input is 12:

"r00gc0+:?!;1-}o{70.

The c0 in the code is changed to add up to input number in hex, up to f+f=30. The challenge didn't specify what to do if the input was out of bounds, so I ignored it.

Let me know if there is anything I can improve on!

Bash, 25 bytes

eval echo\ echo\$_{0..$1}

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///, 65 bytes

/9/8*//8/7*//7/6*//6/5*//5/4*//4/3*//3/2*//2/1*//1/0*//*0/9*//0//

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Converts decimal to unary.

///, 0 bytes

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Takes input as unary. For me, That's cheating.

Julia 1.0, 36 bytes

print('1'^parse(Int,ARGS[]),|>,show)

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port of Jo King's answer

will print something like 1111|>show (equivalent to show(1111))

Raku, 20 18 bytes

say 1 x get,".put"

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Outputs a number with n digits followed by a .put

05AB1E, 5 bytes

1¸sиJ

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Sort-of port of emanresu A's Vyxal answer:

1¸sиJ  # Implicit input                 STACK:
1¸     # Push ['1']                     ['1'], 5
  sи   # Repeat input number of times   ['1', '1', '1', '1', '1']
    J  # Join by ''                     '11111'
       # Implicit output

Retina, 13 bytes

.+
*KKK
KK
K`

Try it online! Explanation: Outputs a string of length n+2 alternating between K and `. This creates a program in Retina that outputs the part of the string after the K` which is also equal to the first n characters of the program. Retina can also execute the resulting program for you automatically: Try it online! Or see both the program and its output: Try it online!

Ruby, 26 bytes

$><<?1*gets.to_i+'=>x;p x'

Uses the Ruby 3 pattern match syntax to bind the integer to x.

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Charcoal, 1 byte

Ｎ

Try it online! Port of @Ausername's Vyxal answer. Explanation: Simply outputs n -s; strings of printable ASCII need no delimiter in Charcoal, so as a program, it just prints the string of -s, i.e. itself.

Python 3, 48 bytes

print('a'*int(input())+'=1;print(locals()[-1])')

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Vyxal, 3 bytes

\1*

Try it Online! Literally prints that many 1s.