I experienced the same issue on Fedora 34.
I used this example file to reproduce the problem:
using System.Drawing;
Bitmap bmp = new Bitmap(200, 100);
using var gfx = Graphics.FromImage(bmp);
gfx.Clear(Color.Navy);
Font fnt = new Font("Arial", 18);
gfx.DrawString("test123", fnt, Brushes.Yellow, 10, 10);
bmp.Save("test.bmp");
(Note that the code above compiles and runs with .NET 5 and C# 9.0 since it supports top-level statements, https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/top-level-statements.)
However, the result looked like this:

What I did to fix this, was to run the following terminal command:
$ dotnet add package system.drawing.common
After that, re-building and running the program yields this image instead:

With this change, my .csproj
file now looks like this:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net5.0</TargetFramework>
</PropertyGroup>
<ItemGroup>
<PackageReference Include="system.drawing.common" Version="5.0.2" />
</ItemGroup>
</Project>
Just for reference; the reason I stumbled upon this problem was when I tried to use ScottPlot, and I filed this bug about it: https://github.com/ScottPlot/ScottPlot/issues/1079