Do you mean a start page as in the page that shows up when you open your browser? If so, you don’t need it to be online. You could just keep it on a folder on your PC and set your browser to open the page file by default. You can do this on mobile as well.
If you want to easily switch between devices, you could host it somewhere for free. Check out the list of resources here on the forum.
As to making it, I think most people just use HTML and CSS. If you’re into making stuff for the web but don’t know those, I really recommend learning. However, there are services that will generate a page for you… again, check out the resources thread. In terms of making a personal dashboard, I’ve also heard of people using Notion or Obsidian for that, but I don’t use them so I can’t give you a more detailed explanation.
If you need inspiration, tips and tricks, etc. check out our very own thread about custom start pages: Custom Startpage!!