You're very close. The main issue is that you wrote the array as [(...)] instead of [...]. In your code, the array only contains one value, if you remove the () you will have three values. See comma operator for details.

The other thing you have to consider is that an async function always returns a promise, so you must await o as well -

(async () =>
  console.log(
    await ["apple", "banana", "orange"].reduce(async (o, fruit) => {
      const rand = new Promise((resolve) => setTimeout(() => resolve(Math.random()), 200))
      return { ...await o, [fruit]: await rand }
    }, {})
  ))();

{
  "apple": 0.8731611352383968,
  "banana": 0.163521266739585,
  "orange": 0.8419246752641664
}

Note reduce as used above will resolve the promises in series (sequentially). Other comments suggesting map->Promise.all will resolve the promises in parallel (simultaneously)

If you add another console log in the reducer you can see what is happening.

(async () =>
  console.log(
    await [("apple", "banana", "orange")].reduce(async (o, fruit) => {
      console.dir({o, fruit})
      const random_number = await new Promise((resolve) => setTimeout(() => resolve(Math.random()), 200));
      return { ...o, [fruit]: random_number };
    }, {})
  ))();

output:

{ o: {}, fruit: 'orange' }
{ orange: 0.39647395383957074 }

This is because you have wrapped your array item in parentheses [("apple", "banana", "orange")] so there is only one item to reduce.

After fixing this the output is

{ o: {}, fruit: 'apple' }
{ o: Promise { <pending> }, fruit: 'banana' }
{ o: Promise { <pending> }, fruit: 'orange' }
{ orange: 0.8347447113637538 }

Now you can see that the promises are not properly awaited. @Mulan already gave the answer for this so I won't repeat it.

I will suggest using map instead of reduce for this. This will stop the promises from blocking one another, in your reduce code the reducer must wait for one promise to complete before moving the the next. If you gather all the promises together and await them using Promise.all you can avoid this.

  (async () => {
    //map the array to an array of promises
    const promises = ["apple", "banana", "orange"].map(async (fruit) => {
      const random_number = await new Promise((resolve) => setTimeout(() => resolve(Math.random()), 200));
      return { [fruit]: random_number };
    });

    //wait for all promises to resolve
    const results = await Promise.all(promises);

    //merge the result objects together
    const result = Object.assign(...results);
    
    console.log(result)
  })();