For single notes you can use Typora - I’m using it to copy notes as HTML and paste them in WordPress’ back-end.
Similarly, you can merge multiple notes - either using one of the available plugins for Obsidian or manually (combining MarkDown files is the same as combining TXTs and can be done with a single command in a terminal) and then go the Typora route.
Of course, this way you lose any inter-linking between notes, and I don’t think images are supported. However, if that’s what you want, exporting hundreds of linked MarkDown notes as HTML while keeping their internal structure/links, then you need a whole different solution that I don’t think even exists.