`eulervm` and bold theorems

Question

I use concrete-roman as in Knuth's Concrete Mathematics as my main font. However, it does not come with a math font, so I include eulervm for it.

\usepackage{amsmath,amssymb,amsthm}
\usepackage{concrete}% the concrete-roman, used in concrete mathetics
\usepackage{eulervm}% the math fonts used in concrete mathematics

This has gone well until I tried to boldify my theorems. Namely, instead of

Theorem 4.1. 1+1 = 2

I want

Theorem 4.1. 1+1 = 2.

For this, I added the following command to header copying from How to make the optional title of a theorem bold with amsthm?

\newtheoremstyle{mystyle}%                % Name
  {}%                                     % Space above
  {}%                                     % Space below
  {}%                                     % Body font
  {}%                                     % Indent amount
  {\bfseries}%                            % Theorem head font
  {.}%                                    % Punctuation after theorem head
  {.5em}%                                    % Space after theorem head, ' ', or \newline
  {\thmname{#1}\thmnumber{ #2}\thmnote{ (#3)}}%                                     % Theorem head spec (can be left empty, meaning `normal')
\theoremstyle{mystyle}
\numberwithin{equation}{subsection}
\newtheorem{theorem}[equation]{Theorem}

It does not work.

If I remove eulervm, then the theorems do get boldified. However, the fonts fall back to some default ones..

Question

How to I remain in the la-la-land of concrete+eulervm fonts, with boldified theorems?

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possibly related

It's pointed out in Bold mathematics in eulervm that eulervm handles bold fonts differently. But they only addressed bold math fonts..

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Minimal example

Below is a minimal example that compiles with $ pdflatex. You can toggle eulervm to see the effects described in my question. Notice that mystyle is indeed working: disabling \theoremstyle{mystyle} changes the font of the body to italic (default).

\documentclass[15pt]{article}
\usepackage[margin=1in]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{amsmath,amssymb,amsthm}
\usepackage{concrete}% the concrete-roman, used in concrete mathetics
\usepackage{eulervm}% the math fonts used in concrete mathematics
\newtheoremstyle{mystyle}%                % Name
  {}%                                     % Space above
  {}%                                     % Space below
  {}%                                     % Body font
  {}%                                     % Indent amount
  {\bfseries}%                            % Theorem head font
  {.}%                                    % Punctuation after theorem head
  {.5em}%                                    % Space after theorem head, ' ', or \newline
  {\thmname{#1}\thmnumber{ #2}\thmnote{ (#3)}}%                                     % Theorem head spec (can be left empty, meaning `normal')
\theoremstyle{mystyle}
\newtheorem{theorem}[equation]{Theorem}
\begin{document}
\begin{theorem}
  The sum of $1$ and $1$ is $2$.
\end{theorem}
\end{document}

Answer 1

After digging a bit into the font description files, I found the reason bold substitutions were not working. Concrete does not come in bold, and the font package only declares a substitution for the /bx/n series and shape in the T1 encoding. By default, you were trying to use /b/n of OT1.

You can therefore replace the command

\usepackage{concrete}

with

\usepackage[T1]{fontenc}
\usepackage{ccfonts}
\renewcommand\bfdefault{bx}

I would recommend you use unicode-math and LuaLaTeX where you can, and legacy 8-bit fonts when you have to, though. See this answer for several longer examples.

Since you are defining your own theorem style, you could instead select the font of your choice for its headers, such as, here, Latin Modern Sans-Serif Semi-bold Condensed:

\documentclass[15pt]{article}
\usepackage[margin=1in]{geometry}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc} % The default since 2018
\usepackage{amsmath,amssymb,amsthm}
\usepackage{bm}
\usepackage{ccfonts}% the concrete-roman, used in concrete mathetics
\usepackage{eulervm,eucal,eufrak}% the math fonts used in concrete mathematics
\renewcommand\bfdefault{bx}
\newtheoremstyle{mystyle}%                % Name
  {}%                                     % Space above
  {}%                                     % Space below
  {}%                                     % Body font
  {}%                                     % Indent amount
  {\usefont{T1}{lmss}{sbc}{n}}%           % Theorem head font
  {.}%                                    % Punctuation after theorem head
  {.5em}%                                 % Space after theorem head, ' ', or \newline
  {\thmname{#1}\thmnumber{ #2}\thmnote{ (#3)}}%                                     % Theorem head spec (can be left empty, meaning `normal')
\theoremstyle{mystyle}
\newtheorem{theorem}[equation]{Theorem}
\begin{document}
\begin{theorem}
  The sum of $1$ and $1$ is $2$.
\end{theorem}
\end{document}