A Meteor Client add-on that shows new chunks on 2b2t.org.
The module is under the "Render" category and is simply named "New Chunks".
What it does is check for Copper Ore blocks over Y 0 in the overworld, which would mean the chunk was generated in 1.19 (post-update). For the nether, it checks for any Ancient Debris blocks.
Disable the module to clear the new chunks' renders.
Probably not. If the server you want to try it on updated from 1.15 or lower to a version 1.16 or higher, it will show chunks that were generated before that update.
Go to the release tab, download the .jar file and put it inside your mods folder in .minecraft.