How to change 'Welcome to your Strapi app' document title

After spending hours, asking here. how and where to change below document titles in strapi

  1. Welcome to your Strapi app
  2. strapi admin

any help is really appreciated

See the public assets part of the documentation:

Basically you can put an index.html in the /public folder and that would be served instead (the current ones are not easily extendable since they come from the node_modules, specifically the strapi package, specifically the public middleware: strapi/packages/strapi/lib/middlewares/public at master · strapi/strapi · GitHub