Pixel 4a Water damaged. Phone isn't turning on. Please help.

Hi. My Pixel 4a got damaged when I was soaked in rain. Even though phone was inside the pocket, some water went inside. I didn't notice it at 1st. Then camera started to fog which is when I realised. When there came an error & warning messages, all the ports got disabled. I immediately wrapped it up in tissue papers & kept it inside rice for a day. It didn't recover, but the touch screen started to act weird. I touch somewhere, & something else gets operated. Then I immediately took all the backup the data.

Gave it to a local mechanic. He opened up the phone. Let out all the remaining water & told there were lots of water in it, But battery is good, some parts are short circuited. After drying it thoroughly, worked for a brief moment. All the ports were working fine & touch was still weird. When I switched off the phone, problem started again. The real problem. Its not Turing on. It just comes to Fast Boot Mode & doesn't proceeds further. It doesn't even proceeds to Recovery mode or Rescue mode by pressing volume buttons. It just stays there in Fast Boot Mode untill the battery drains.

To repair that, Google Authorised service centre charges almost similar price of the phone itself. Please help me. I'm attaching it's photo. If I can get any help to recover my phone, that would mean a lot to me.

Thank you for help.