How to disable HTML on the forum?

[Canapin (Coin-coin le Canapin)]

You can try using this plugin:

Discourse Fingerprint - Browser Fingerprinting Plugin

Discourse Fingerprint Discourse Fingerprint comes as a tool to community managers in their combat with internet trolls. It works by computing a unique identifier (a fingerprint) of each registered user, by taking into consideration over 20 browser characteristics such as user agent, screen resolution, timezone, device memory, etc. When each of these browser characteristics are considered separately, they are not enough to assess whether two users are the same. There is a …

In short, it helps identify users using multiple accounts based on their software.