documentclass[12pt]{article}
usepackage[english]{babel}
usepackage[utf8]{inputenc}


usepackage[
backend = biber,
style = apa,
defernumbers=false,
uniquelist=true]{biblatex}
DeclareLanguageMapping{english}{american-apa}

usepackage{xpatch}

AtEveryCitekey{ifciteseen{}{clearfield{namehash}}}

xpatchbibmacro{cite}
  {printnames{labelname}}
  {ifciteseen
     {printnames{labelname}}
     {printnames[][1-99]{labelname}}}
  {}
  {}

 xpatchbibmacro{textcite}
  {printnames{labelname}}
  {ifciteseen
     {printnames{labelname}}
     {printnames[][1-99]{labelname}}}
  {}
  {}


addbibresource{dummy_lit.bib} %name of the .bib file with my references

begin{document}

I would like to have the abbreviation "et. al" in the running text whenever the references have more than three authors and not this:

textcite{Author2000}


end{document}

@Article{Author2000,
   author       =  {Last name1, Firstname 1 and Last name2, First name2 and Last name3, First name3 and Last name4, First name4 and Last name5, First name5},
   title        =  {The title of my article},
   journal      =  {The journal},
   year         =  {2000},
   volume       =  {1},
   number       =  {2},
   pages        =  {1-10},
   keywords     =  {ref}
}