Why do my headphones sometimes connect to my laptop with audio only and other times with both audio and microphone?

I connect my Bose QC35 II headphones via Bluetooth with my MSI GS76 Stealth 11UH (mirror) laptop running Windows 11 24H2 Pro.

Sometimes the headphones are connected with audio only:

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Sometimes the headphones are connected with both audio and microphone:

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Why do my headphones sometimes connect to my laptop with audio only and other times with both audio and microphone?