I can't put my finger on it, but BRK feels like it's behaving differently. I don't know if it is just that Buffett is a bit depressed after losing his close friend

This is the one option I would exclude 100%. Why? Because while Warren might(?) be depressed in my book he is the very last person to let himself be even a tiny bit influenced by that with respect to his duties and responsibilities toward his partners (us). I have far to much respect for him, for his rationality and integrity, to think for a moment this could be a reason for whatever action or non-action by him.

I personally think the most simple explanation is the most likely one: That he sees nothing really attractive and simply prefers to wait, that he feels again like the "oversexed guy in the desert". Would perfectly fit my picture of him as being the opposite of a "FOMO" type, without problems to wait and wait and wait until the harem appears.

This does not even require
I don't know if they sense a major shift in the markets and are quietly and rapidly preparing for it
as I picture Warren as thinking in this respect "Maybe a crash comes, maybe not. Trying to forecast that is a silly game in which I don't need to participate. I don't see good opportunities right now, that's all I need to know. So I wait and all else remains to be seen"