Markdown (in parse modes Markdown, MarkdownV2) doesn't work in Telegram webhook because all markdown symbols are escaped after the fix in ZBX-20150. Now these modes are documented and thus must work properly.

Even though ZBX-20150 reported the problem about markdown symbols in macro values (such symbols should be escaped indeed) the fix escaped all characters in the message altogether so now there is no way to send markdown-formatted messages.

Zabbix should resolve this by either:

1. Reverting the fix from ZBX-20150 and documenting the advice not to use Markdown/MarkdownV2 if macro values (e.g. host names) contain special characters.
2. Removing official support of parse modes Markdown and MarkdownV2. Supported parse modes will be empty or HTML in this case.
3. Introducing macro functions that escape values for the given macros. This option is a massive amount of work and should be a subject of a separate feature request.