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Updating to a supported kernel like 6.7 stable, 6.6 LTS (Long Term Support) or 6.1 LTS is what you need to do. 6.8 is an RC (Release Candidate) and should not be used for daily use.
Maybe you typed the command wrong? See Manjaro Kernels - Manjaro
Here’s an easy way: [HowTo] use public command-line pastebin services without installing anything!
Such as manjaro-chroot?
Please also see the following for reference: