⠀⠀⠀ Steam won't let you remove achievements from your showcase once you've added them.
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀ This provides a method to do so.




⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀Go to your profile's edit showcase page in a browser.
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀steamproxy.net/my/edit/showcases


⠀⠀⠀⠀⠀⠀⠀Locate the achievement you wish to remove from your achievement showcase.
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀Right click it, then click the inspect elements button.



⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀You should see some code that looks similar to what is below.

<input type="hidden" name="rgShowcaseConfig[17][0][appid]" value="209330">
<input type="hidden" name="rgShowcaseConfig[17][0][title]" value="2_4">

⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀Simply change the two values at the end to zero.

<input type="hidden" name="rgShowcaseConfig[17][0][appid]" value="0">
<input type="hidden" name="rgShowcaseConfig[17][0][title]" value="0">

⠀⠀⠀⠀⠀⠀⠀⠀ Go ahead and close the console, then save the page, then refresh the page.