Have you looked at d2lang - it supports SVG output:
https://d2lang.com/tour/exports/
The syntax is a bit different though, so it depends on where your source is coming from, see here: https://text-to-diagram.com/?example=sequence&b=mermaid
The syntax is a bit different though, so it depends on where your source is coming from, see here: https://text-to-diagram.com/?example=sequence&b=mermaid
However the big problem here being that d2 is still quite new and isn't as well supported as Mermaid JS