Vendroid is a custom Discord client for Android. The way it works is that it loads the discord.com website and injects Vencord.
Discord's mobile site is not very usable since it has many issues. As such, this is mostly just a proof of concept and is not really maintained.
You are likely better off using Aliucord or Vendetta, that are proper mods of the old and new Discord Android app respectively
Visit the latest release, grab the apk and install it