Custom font with bold

cmr means roman font, you should use cmb

fontauthfont=cmb10 at 10pt

author{%
authfont%
...
}

As you are not providing full MWE, I just corrected the error in your code...

The template is publicly available and the sample .tex file starts with

documentclass[11pt,a4paper]{article}
usepackage[hyperref]{emnlp2020}
usepackage{times}
usepackage{latexsym}
renewcommand{UrlFont}{ttfamilysmall}

% This is not strictly necessary, and may be commented out,
% but it will improve the layout of the manuscript,
% and will typically save some space.
usepackage{microtype}

%aclfinalcopy % Uncomment this line for the final submission
%defaclpaperid{***} %  Enter the acl Paper ID here

%setlengthtitlebox{5cm}
% You can expand the titlebox if you need extra space
% to show all the authors. Please do not make the titlebox
% smaller than 5cm (the original size); we will check this
% in the camera-ready version and ask you to change it back.

newcommandBibTeX{Btextsc{ib}TeX}

title{Instructions for EMNLP 2020 Proceedings}

author{First Author 
  Affiliation / Address line 1 
  Affiliation / Address line 2 
  Affiliation / Address line 3 
  texttt{email@domain} And
  Second Author 
  Affiliation / Address line 1 
  Affiliation / Address line 2 
  Affiliation / Address line 3 
  texttt{email@domain} }

date{}

begin{document}
maketitle

The result will be

and this is what the conference managers want. Don't try to override the standard they want.

If I uncomment the aclfinalcopy line, the result is

The font for the author part is 12pt and is automatically bold for the author name, medium weight for the affiliation, even larger than what you're trying to get and it is Times, as per the instruction usepackage{times}.