What happened with “Number of CPU threads” option in 7-ZIP?

I have a .tar file that I want to compress into .gz file. I don’t know why but the option Number of CPU threads of 7-Zip 25.01 (x64) does not work on my Windows 11 Pro 25H2, i.e., the option Number of CPU threads is greyed-out (disabled) and therefore there is no drop-down list to choose:

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Could you explain on this issue?