Here's the pictures I screenshot.
Also, can you show me the tutorial about Make-your-own-game kit for Web and Dreamcast? I got confused about reading.
Ok, I think I recorgnize the errors:
For the Dreamcast error, it looks like the disc title is too long. If your command is something like "make_cdi.bat GameTitle DISC_TITLE", it's the DISC_TITLE causing the issues, try using a shorter one, that should do the trick. I'm not sure if it's a CD limitation or of the program making the cd image, but I also ran into this issue before.
For the web version, it looks like you are trying to open the index.html in your folder locally, without uploading it to itch or a similar site first. Browsers don't like loading local files (due to security reasons) and want all files to have either a http:// or https:// path. The easiest way to emulate that is to create a test project on itch and upload the zip there (you can make a project without publishing it and test there). It also seems to work locally with the Edge browser because it does not have the security check against loading local files I mentioned before.
Both Make-Your-Own-Game-Kits come with a README.txt, that is all the documentation there is right now. I'll add it to the regular Dolmexica documentation for next time and add a note about the two issues you encountered. I hope the rest of it works as expected now, once again sorry about the errors.