Recently released tzdata2024b includes:
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      The main source files' time zone abbreviations now use %z,
      supported by zic since release 2015f and used in vanguard form
      since release 2022b. For example, America/Sao_Paulo now contains
      the zone continuation line "-3:00 Brazil %z", which is less error
      prone than the old "-3:00 Brazil -03/-02". This does not change
      the represented data: the generated TZif files are unchanged.
      Rearguard form still avoids %z, to support obsolescent parsers.
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Those "%z"s need to be replaced with the GMT format at runtime, otherwise they will appear literally.