Alright, as promised here is how I did it:
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Create a text file that contains (replace location as needed)
C:\Windows\System32\cmd.exe /C start “” /affinity F0 “C:\Program Files (x86)\Steam\Steam.exe” -
Rename its extension to .cmd or .bat.
You can double click the file to start steam or -
Open Run (Windows key + R) and enter “shell:startup” (opens the startup folder in win10).
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Move the file there to automatically run it on startup.
About the affinity value:
I have 8 logical cores (would be 16 with SMT enabled) which can be represented with 8 bits. If I wanted to enable, let’s say only the 2nd core it would correspond to “00000010” and after converting it from binary to hex it becomes “2”.
I’m using “11110000” -> “F0”.
I’ll try to test later which change actually helped me.