amtierend
incumbent
Currently holding an official office or function; being in office.
Der amtierende Präsident wird bei der nächsten Wahl nicht erneut kandidieren.
The incumbent president will not run again in the next election.

incumbent
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incumbent
Currently holding an official office or function; being in office.
Der amtierende Präsident wird bei der nächsten Wahl nicht erneut kandidieren.
The incumbent president will not run again in the next election.

'Amtierend' (incumbent) is the present participle of the verb 'amtieren' (to hold office). This verb, in turn, is derived from the noun 'das Amt' (the office).
Er amtiert seit vier Jahren als Schatzmeister des Vereins.
He has held office as treasurer of the association for four years.
This adjective is used almost exclusively attributively, meaning directly before a noun. Predicative use (e.g., 'Der Bürgermeister ist amtierend.' — The mayor is incumbent.) is very unusual.
Die amtierende Weltmeisterin verteidigte ihren Titel erfolgreich.
The incumbent world champion successfully defended her title.
The word 'amtierend' (incumbent) belongs to formal language and is mainly used in politics, administration, business, and reporting on those areas.
Der amtierende Vorstandsvorsitzende gab die neuen Unternehmensziele bekannt.
The incumbent CEO announced the new corporate goals.
current
'aktuell' and 'amtierend' both refer to the present. 'aktuell' is general and can be used for many things: 'aktuelle Nachrichten' (current news), 'aktuelle Probleme' (current problems), or 'der aktuelle Plan' (the current plan). 'amtierend' is used only for people who are currently holding an official office or a specific function. So it fits roles such as president, mayor, chairperson, or champion. If you generally mean 'valid or important right now', 'aktuell' is correct. If you mean a person in their current office, 'amtierend' is more precise.

Zur Begrüßung sprach die amtierende Bürgermeisterin über die neuen Pläne der Stadt.
In her welcoming remarks, the incumbent mayor spoke about the city's new plans.
Die Lehrerin hat uns den aktuellen Stundenplan für morgen gezeigt.
The teacher showed us the current timetable for tomorrow.