[majkinetor]

Core redocly is free. To have any more serious customization, you need to pay significantly.

Also, I highly appreciate redoclys starter template which tackles more serious topic about developing API first with reusable components instead of writing everything in one big file is is nightmare.

[CharlieDigital]

RapiDoc is quite nice and built with Lit so it sets up as just a custom web component.

Very customizable in my experience (working with it with .NET SwaggerGen tooling).