Oh, so turns out #unity has introduced a terrain shadow bug somewhere between 2022.3.7 and 2022.3.62, i.e. in the "critical bugfixes only!" LTS release train. Nothing related mentioned in the release ...
...aaand closed with "lol sorry, won't fix" :/ https://issuetracker.unity3d.com/issues/terrain-shadows-changing-shape-when-they-are-viewed-at-a-different-angle-from-the-same-position
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