Tried everything to opt out of the Minecraft Beta on PC - NOTHING works.

Have you opted out of the beta in the xbox insiders hub?

You need to opt out then unistal Minecraft then re install

I tried, but it didn't work.

I tried also to wait for some hours but when I reinstalled Minecraft I got the beta.

Once you opt out of beta and then uninstall it, you shouldn't be able to install beta without opting back in. You must restart console before installing normal minecraft. Then try installing normal version and see if multiplayer works.

Have you opted out of the beta in the xbox insiders hub?

You need to opt out then unistal Minecraft then re install

Opting into and out of beta:

1. Xbox One and Windows 10 players can opt in and out of the beta from the Xbox Insider Hub app. Please be aware that opting in and out of the beta may affect all user accounts on a shared device*.
2. Android players can opt in and out from the Minecraft page of the Google Play Store.
3. Please bear in mind that un-enrolling from the Minecraft Beta can sometimes take up to 24 hours
   

Source: https://feedback.minecraft.net/hc/e...8671-How-to-Join-and-leave-the-Minecraft-Beta

Edit:

There are more detailed instructions at this link: https://news.xbox.com/en-us/2018/07/09/minecraft-beta-guide-and-faqs/

You need to opt out of insider on your xbox and then delete minecraft beta and install minecraft full