https://tex.stackexchange.com/q/569554/35864

parencitedot.tex

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage{csquotes}

\usepackage[backend=biber, style=authoryear]{biblatex}

\renewcommand*{\postnotedelim}{\addcolon\space} % add colon after year on \parencite
\DeclareFieldFormat{postnote}{#1} %no page prefix when citing
\DeclareFieldFormat{multipostnote}{#1} %no page prefix when citing


\begin{filecontents}{\jobname.bib}
@book{elk,
  author    = {Anne Elk},
  title     = {A Theory on Brontosauruses},
  year      = {1972},
  publisher = {Monthy \& Co.},
  location  = {London},
}
\end{filecontents}
\addbibresource{\jobname.bib}
\addbibresource{biblatex-examples.bib}

\begin{document}
Lorem \parencite[380]{sigfridsson}
ipsum \parencite[42]{elk}

\printbibliography
\end{document}