the default blazor server template comes with the bootstrap CSS installed in wwwroot. Your CSS load errors appear to due to your wwwroot not being correct. You appear to have multiple loads of bootstrap and your site.css is not found.
You should not install or use the Bootstrap javascript file as it is not supported with virtual dom technologies like Blazor or react.
this means several of the bootstrap components will not work without writing Blazor support code.
for a Modal, your blazor code should add and remove the bootstrap classes to show and hide a modal. you will need to add blazer click handlers for the buttons and close icon if rendered.
there is really not a lot of need for jQuery with a blazor project either.
as you appear to be using Radzen controls, why bootstrap?