TOC with section* AND alpha (A, B, C, etc) subsection labels

I have two tasks I’m trying to accomplish, both of which I found independent solutions for on other threads. However, when the solutions are used in combination they conflict so I’m looking for an approach that is compatible with both

Task 1: use alpha labels for subsections (i.e. A, B, C, etc). This can be accomplished with renewcommandthesubsection{Alph{subsection}} as suggested in @GonzaloMedina’s answer

Task 2: automatically add section* entries to the TOC. This answer by @egreg suggests sticking with plain section and using setcounter{secnumdepth}{0} to remove the numbering in the TOC

If I were able to successfullly combine these two tasks (which I haven’t), my desired rendering would look like the following

However, using @egreg’s solution for task 2 causes the A, B, C subsection labels to disappear. I tried another suggestion from the same thread by @MikeRenfro to add renewcommand{thesection}{}, but as the author mentions, it leaves unnecessary indents which are not aesthetically pleasing. On a separate thread, @Vser suggests addcontentsline{toc}{section}{nameref{sec:intro}}, but in my testing this left a line of pure ... without auto-populating the section name. The manual work to enter each name without the help of nameref would be too time-consuming and difficult to maintain.

EDIT 7/28/20: In my actual document, I’m using tcolorbox to help visually define the section headers. For instance, the following MWE along with it’s rendering

documentclass[a4paper,10pt,twocolumn]{book}
usepackage{cuted}
usepackage{tcolorbox}
usepackage[explicit]{titlesec}

setcounter{tocdepth}{1}
titlespacing*{section}{0pt}{0pt}{0pt}
titleformat{name=section, numberless}{setcounter{subsection}{0}normalfontLargebfseries}{}{0pt}{}[addcontentsline{toc}{section}{#1}#1]
renewcommandthesubsection{Alph{subsection}} % Accomplishes task 1

begin{document}
    
    tableofcontents
    chapter{Chapter}

    begin{strip}
        begin{tcolorbox}[title=section*{An unnumbered section}]
            Other content here..
        end{tcolorbox}
    end{strip}
    subsection{First Subsection}   
    subsection{Second Subsection}  
    
end{document} 

Originally, I had included titlespacing*{section}{0pt}{0pt}{0pt} in the preamble to ensure there was no extra space above, below, or left of the section title text. However, the current solution by @Bernard adds an extra blank row above the section header as seen in the rendering

documentclass{book}
usepackage[explicit]{titlesec,}

setcounter{tocdepth}{1}
titlespacing*{section}{0pt}{0pt}{0pt}
titleformat{name=section, numberless}{setcounter{subsection}{0}normalfontLargebfseries}{}{0pt}{}[addcontentsline{toc}{section}{#1}#1]
renewcommandthesubsection{Alph{subsection}} % Accomplishes task 1

begin{document}

    tableofcontents
    chapter{Chapter}
    section{A numbered section}
        subsection{Subsection}
    section*{An unnumbered section}

end{document}