Hi and welcome to the community!
I'm using the 2022.2.22 version, but I'd expect it to behave the same was as the version you're using.
What I did to create a welcome page that doesn't show up in the Toc was:
1. Create a ToC that does not include the welcome page (but with all the other topics I want to include).
2. On the HTML5 output preset > Content tab,
2a. Select the ToC just created.
2b. Set the welcome topic as the Default Topic.
3. Generate the HTML5 doc.
The default topic now shows in the main content pane when I open the HTML doc but doesn't appear in the ToC.
Hope this helps!