apa style and citing both in text as at the end of a sentence

You could use biblatex, the apa style and natbib citation styles.

(citefield{A-reference}{title} from biblatex)

Try this code.

documentclass[12pt,a4paper]{article}

begin{filecontents}[overwrite]{jobname67.bib}
@article{einstein,
    author =       "Albert Einstein",
    title =        "{Zur Elektrodynamik bewegter K{"o}rper}. ({German})
    [{On} the electrodynamics of moving bodies]",
    journal =      "Annalen der Physik",
    volume =       "322",
    number =       "10",
    pages =        "891--921",
    year =         "1905",
    keywords =     "physics"
}
        
    @book{knuth,
        author       = {Knuth, Donald E.},
        title        = {The {TeX book}},
        date         = 1984,
        maintitle    = {Computers & Typesetting},
        volume       = {A},
        publisher    = {Addison-Wesley},
        location     = {Reading, Mass.},
        langid       = {english},
        langidopts   = {variant=american},
    }   
    
    @book{companion,
        author       = {Goossens, Michel and Mittelbach, Frank and Samarin, Alexander},
        title        = {The {LaTeX} Companion},
        date         = 1994,
        edition      = 1,
        publisher    = {Addison-Wesley},
        location     = {Reading, Mass.},
        pagetotal    = 528,
        langid       = {english},
        langidopts   = {variant=american},
    }
    
end{filecontents}

usepackage{csquotes}
usepackage[backend=biber,
language=auto,
style=apa,
natbib=true]{biblatex}

addbibresource{jobname67.bib} %<<<<<<<<<<<<<<<<<

begin{document}

In this document there are three cited items:

textit{citefield{companion}{title}}  book citep{companion}, the citeauthor{einstein}'s journal paper (citeyear{einstein}) and other LaTeX related items  like citet{companion} and a nice citeauthor{knuth}`s book citep{knuth}.

printbibliography  
    
end{document}