Is Minecraft beta now the same version as the non beta after the "Nether update" was released?

No, it is not the same, the beta version will be updated soon with new features

The beta version will be updated shortly. though if you wanted to speed things up you could play on the normal version

I have found a solution. After I deleted my original insider account I created a new one and joined the rtx minecraft beta other than the nether beta which was what I was in. I then updated minecraft to rtx and unenrolled and reverted back to the normal
minecraft version.

According to https://minecraft.gamepedia.com/Bedrock_Edition_beta_1.13.0.1 it seems you opted in to recieve BETA updates to Minecraft.

As Beta versions are test versions and might contain unstable code, public servers do not update to Beta versions.

So if you wish to use public servers, make sure you only use non-Beta versions of Minecraft. If necessary, un-enroll from the Minecraft Insider Beta program, and wait until the next official update, or uninstall and re-download the latest public non-beta
version of Minecraft.

Hello!

If you opted into the Minecraft Beta, then you removed yourself from the beta program, your game will still stay on the latest Beta version. You would need to uninstall and reinstall the game to get on the latest full (non beta) release.