Variation on my CollectionEditingHtmlExtensions gist to use TagHelper instead.

CollectionItemTagHelper.cs

[HtmlTargetElement("CollectionItem")]
public class CollectionItemTagHelper : TagHelper
{
    private readonly IHtmlHelper htmlHelper;

    [ViewContext]
    [HtmlAttributeNotBound]
    public ViewContext ViewContext { get; set; }

    public CollectionItemTagHelper(IHtmlHelper htmlHelper)
    {
        this.htmlHelper = htmlHelper;
    }
    [HtmlAttributeName("name")]
    public string CollectionName { get; set; }

    [HtmlAttributeName("index")]
    public string IndexValue { get; set; }

    public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
    {
        if (CollectionName == null)
            throw new ArgumentNullException(nameof(CollectionName), "CollectionName is null");
        if (string.IsNullOrEmpty(IndexValue))
            throw new ArgumentException("IndexValue is null or empty", nameof(IndexValue));

        //Needed to initialize the htmlHelper
        (htmlHelper as IViewContextAware).Contextualize(ViewContext);

        //suppress rendering of the TagHelper element itself
        output.TagName = null;

        //a hidden <input> element to hold the current index value passed in
        var indexField = new TagBuilder("input");
        indexField.MergeAttributes(new Dictionary<string, string>() {
            { "name", htmlHelper.ViewData.TemplateInfo.GetFullHtmlFieldName(CollectionName != string.Empty ? $"{CollectionName}.Index" : "Index") },
            { "value", IndexValue },
            { "type", "hidden" },
            { "autocomplete", "off" }
        });

        //Write the hidden <input> element
        output.PreElement.AppendHtml(indexField);

        using (new CollectionItemNamePrefixScope(htmlHelper.ViewData.TemplateInfo, htmlHelper.ViewData.TemplateInfo.GetFullHtmlFieldName($"{CollectionName}[{IndexValue}]")))
        {
            output.Content.SetHtmlContent(await output.GetChildContentAsync());
        }
    }
    private class CollectionItemNamePrefixScope : IDisposable
    {
        private readonly TemplateInfo _templateInfo;
        private readonly string _previousPrefix;

        public CollectionItemNamePrefixScope(TemplateInfo templateInfo, string collectionItemName)
        {
            _templateInfo = templateInfo;
            _previousPrefix = templateInfo.HtmlFieldPrefix;
            templateInfo.HtmlFieldPrefix = collectionItemName;
        }

        public void Dispose()
        {
            _templateInfo.HtmlFieldPrefix = _previousPrefix;
        }
    }
}