I can see that in Foundation for .NET 5 they have usage through .Require

using EPiServer.Framework.Web.Resources;
using EPiServer.Web.Mvc;
using Foundation.Features.Shared;
using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace Foundation.Features.Blocks.Healthbot
{
    public class HealthChatBotBlockController : AsyncBlockComponent<HealthChatbotBlock>
    {
        private readonly IRequiredClientResourceList _requiredClientResourceList;

        public HealthChatBotBlockController(IRequiredClientResourceList requiredClientResourceList)
        {
            _requiredClientResourceList = requiredClientResourceList;
        }

        protected override async Task<IViewComponentResult> InvokeComponentAsync(HealthChatbotBlock currentBlock)
        {
            _requiredClientResourceList.Require(HealthBotClientResourceProvider.BotJs).AtHeader();
            var model = new BlockViewModel<HealthChatbotBlock>(currentBlock);
            return await Task.FromResult(View("/Features/Blocks/HealthBot/HealthChatBotBlock.cshtml", model));
        }
    }

    [ClientResourceProvider]
    public class HealthBotClientResourceProvider : IClientResourceProvider
    {
        public static string BotJs = "healthbot.webchat";

        public IEnumerable<ClientResource> GetClientResources()
        {
            return new[]
            {
                new ClientResource
                {
                    Name = BotJs,
                    ResourceType = ClientResourceType.Html,
                    InlineContent = @"<script crossorigin=""anonymous"" src=""https://cdn.botframework.com/botframework-webchat/latest/webchat.js""></script>"
                }
            };
        }
    }
}

Thanks for helping, Scott!

No luck, though.

I tried with a separate IClientResourceProvider, but requiring the script in InvokeComponentAsync doesn't result in the script being loaded.

However, if I add IClientResourceRegistrator, the script gets loaded - but that defeats the purpose since it results in the script being loaded regardless of whether my block type is rendered on the page.

[ClientResourceProvider]
public class MyResourceProvider : IClientResourceProvider
{
    public static string ResourceName = "someResource";

    public IEnumerable<ClientResource> GetClientResources()
    {
        return new[]
        {
            new ClientResource
            {
                Name = ResourceName,
                ResourceType = ClientResourceType.Script,
                Dependencies = new List<string> { "someDependency" },
                Path = "https://temp.uri/somescript.js"
            }
        };
    }
}

[ClientResourceRegistrator]
public class ClientResourceRegister : IClientResourceRegistrator
{
    public void RegisterResources(IRequiredClientResourceList requiredResources)
    {
        // Always results in the script being loaded (not just when a ContactFormBlock is rendered on the page)
        requiredResources.Require(MyResourceProvider.ResourceName);
    }
}

public class ContactFormBlockViewComponent : AsyncBlockComponent<ContactFormBlock>
{
    private readonly IRequiredClientResourceList _requiredClientResourceList;

    public ContactFormBlockViewComponent(IRequiredClientResourceList requiredClientResourceList)
    {
        _requiredClientResourceList = requiredClientResourceList;
    }

    async protected override Task<IViewComponentResult> InvokeComponentAsync(ContactFormBlock currentContent)
    {
        // Does not result in script being loaded
        _requiredClientResourceList.RequireScript(MyResourceProvider.ResourceName);

        return await Task.FromResult(
            View("~/Features/ContactForm/ContactForm.cshtml", currentContent)
        );
    }
}

@Ted, as far as I know, I don't think you can register client resources from a Component.

You can do it from a controller:

_requiredClientResourceList.Require("fancy_script")
                         .AtHeader();

Failed to get this to work, and instead went with a rather hacky solution that hurts my eyes...

In a nutshell: the Razor page model determines if the page includes blocks that require specific client resources.

public class OnePagerModel : RazorPageModel<OnePager>
{
    private readonly IRequiredClientResourceList _requiredClientResourceList;

    public OnePagerModel(IRequiredClientResourceList requiredClientResourceList)
    {
        _requiredClientResourceList = requiredClientResourceList;
    }

    public void OnGet()
    {
        // Iterate over blocks in a content area to see if there are any blocks that require specific client resources

        var contentAreaContents = CurrentContent.MyContentArea.FilteredItems.Select(x => x.GetContent());

        if (contentAreaContents.Any(x => x is ContactFormBlock))
        {
            _requiredClientResourceList.Require("contactFormBlock").StylesOnly().AtHeader();
            _requiredClientResourceList.Require("contactFormBlock").ScriptsOnly().AtFooter();
        }
    }
}

This is a known issue. Requiring resources from a partial view/compontent has stopped working in CMS12. The fix will be released in 12.4.0 https://world.optimizely.com/support/Bug-list/bug/CMS-21308.