vorgeschlagen
proposed
Describes a person, idea, or plan that has been put forward for discussion, review, or acceptance.
Der vorgeschlagene Kompromiss wurde von beiden Parteien akzeptiert.
The proposed compromise was accepted by both parties.

proposed
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proposed
Describes a person, idea, or plan that has been put forward for discussion, review, or acceptance.
Der vorgeschlagene Kompromiss wurde von beiden Parteien akzeptiert.
The proposed compromise was accepted by both parties.

'Vorgeschlagen' (proposed) is the past participle of the separable verb 'vorschlagen' (to propose). It is very often used like an adjective before a noun to describe an idea or plan that has been presented.
Alle waren mit dem vorgeschlagenen Termin einverstanden.
Everyone agreed to the proposed date.
As an adjective, 'vorgeschlagen' (proposed) usually stands directly before the noun it describes. In this position, it is declined like any other adjective.
Die vorgeschlagene Route führte durch die Berge.
The proposed route led through the mountains.
The word is often combined with abstract nouns that represent an option or idea. Typical examples are: ein vorgeschlagener Plan (a proposed plan), eine vorgeschlagene Lösung (a proposed solution), or ein vorgeschlagener Kandidat (a proposed candidate).
Die vorgeschlagene Lösung schien allen am besten zu gefallen.
The proposed solution seemed to please everyone the most.
planned
'geplant' and 'vorgeschlagen' can both occur with ideas, dates, or plans. The difference lies in the status of the matter: 'geplant' means that something has already been prepared or set as an intention. 'vorgeschlagen' only means that someone has put forward an idea for discussion. It has not necessarily been decided yet. The words can be confused because a proposed date can later become a planned date. If it is only about an idea, 'vorgeschlagen' fits better; if it is already being organized, 'geplant' fits better.

Der vorgeschlagene Treffpunkt ist noch nicht von allen bestätigt.
The proposed meeting point has not yet been confirmed by everyone.
Der geplante Ausflug findet am Samstag statt, wenn das Wetter gut bleibt.
The planned outing will take place on Saturday if the weather stays good.