Python 3, <strike>44</strike> <strike>43</strike> <strike>41</strike> <strike>37</strike> <strike>25</strike> 24 Bytes
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<strike>I have refactored it a ton and came to this answer:

`print(*[x*2 for x in input()],sep="")`

[Try it online!](https://tio.run/##K6gsycjPM/7/v6AoM69EQyu6QstIIS2/SKFCITMPiApKSzQ0Y3WKUwtslZQ0//93yS9NyklVKC5ITcxWBAA)

<strike>then from there I got to
`lambda i:[x*2 for x in i]`
</strike>
<strike>

The TIO doesn't work properly due to it being a function but here it is anyways:</strike> The TIO now works thanks to des54321 for their advice:

[Try it online!](https://tio.run/##K6gsycjPM/6fZhvzPycxNyklUSHTKrpCy0ghLb9IoUIhM08hM/Z/QVFmXomGVpqGkkt@aVJOqkJxQWpitqKSpk5xaoGtkpLmfxRxAA)



Here's my other implementation of this challenge with greatly appreciated help from the comments:

`print("".join(map(lambda x:x*2,input())))`

[Try it online!](https://tio.run/##K6gsycjPM/7/v6AoM69EQ0lJLys/M08jN7FAIycxNyklUaHCqkLLSCczr6C0REMTCP7/d8kvTcpJVSguSE3MVgQA)
</strike>

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End result as of 26/05/2022 thanks to everybody's changes `lambda i:[x*2for x in i]`

[Try it online!](https://tio.run/##K6gsycjPM/6fZhvzPycxNyklUSHTKrpCyygtv0ihQiEzTyEz9n9BUWZeiYZWmoaSS35pUk6qQnFBamK2opKmTnFqga2SkuZ/AA)


Description
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It works by separating the script using pythons map function to grab every character in the inputted string then multiplying them by 2 and joining them back together after it is converted to a map using an empty string then joining every element to it.


Thanks to pxeger for suggesting to remove unnecessary spaces, to Wheat Wizard ♦ for suggesting to remove the quotes from the input, to des54321's advice of using f=\ in the header to fix TIO with lambda functions and Nobody's help detecting the unnecessary space in the lambda.