Parse proxy strings to array of objects
A couple of small comments:
Don't call your parameter the same thing as its type string: string. This makes the code needlessly difficult to read - don't make the reader waste time wondering whether this string a type or the variable. Use input, source or something else that makes sense.
Don't shadow outer variables/arguments in arrow functions, again this harms readability rawArray.map((string) =&gt; fixProxyString(string));. Note that the parenthesis are optional for one parameter too. Consider instead:
function parse(input: string): Proxy[] {
    const rawArray = stringToArray(input);
    const fixedArray = rawArray.map(raw =&gt; fixProxyString(raw));
    const proxyArray = fixedArray.map(fixed =&gt; stringToProxy(fixed));
    return proxyArray;
}

I think (although not tested) that you can further simplify:
function parse(input: string): Proxy[] {
    return stringToArray(input)
        .map(fixProxyString)
        .map(stringToProxy);
}

You don't need to replace and then split here return string.trim().replace(/[ ,\n]+/g, &quot;,&quot;).split(&quot;,&quot;);. You can just split by the regex directly.