Can I use 20w fast charger to charge iPhone 8 Plus?

Google is not a good place to go for answers on almost anything, but especially technical questions. From Google I know:

• That the Earth is flat
• That aliens abduct Earthlings
• That the California forest fires were started by space lasers
• That I should inject bleach to cure COVID-19
• That Elvis Presley is alive
• That the lunar landing missions were a hoax

…need I go on?

The correct place for a technical question is the support link for manufacturer of the product you need information about, their FAQ database or their user forum, as you finally did. But you only need to ask once, not multiple times. Did you expect a different answer the 2nd time?

Manvitha_reddy wrote:

Sir, when I was finding about my phone’s compatibility with 20w charger usage, I was getting different answers from different google’s articles about battery draining. I was little bit confused since I already placed an order for 20w charger without any knowledge and I do have to avoid things if it affect my phone right?

Getting multiple sources for your answer does not address the fact that you questioned the answers given here. In multiple posts. For us, this is maddening behaviour.

If you don't trust this Apple centric community, that's fine. Your choice.

Let's face it, given enough time, you can get any answer you wish using Google.

Yes you can.

Yes. Fast charge your iPhone - Apple Support

Yes.

Have you considered asking a 3rd time to see if you get a different answer?

As I answered in your other post, no.