Η εκδήλωση ενδιαφέροντος έγινε ηλεκτρονικά.

The subject is Η εκδήλωση ενδιαφέροντος.

• Η = the (feminine singular, nominative)
• εκδήλωση = expression / declaration / manifestation
• ενδιαφέροντος = of interest

So the whole subject phrase means the expression of interest.

Because Greek uses the genitive here to express the idea of of.

• το ενδιαφέρον = the interest (dictionary form, nominative)
• του ενδιαφέροντος = of the interest (genitive)

In the phrase εκδήλωση ενδιαφέροντος, the second noun tells you what kind of expression it is: an expression of interest. This is a very common Greek pattern.

Because in Greek, especially in fixed or formal expressions, the second noun often appears without an article.

So:

• εκδήλωση ενδιαφέροντος = expression of interest
• η εκδήλωση του ενδιαφέροντος would sound more specific, like the expression of the interest, and is less natural in this bureaucratic phrase

The version without the article is the standard set expression.

Literally, it means expression/declaration of interest.

In real usage, though, it is often a formal administrative phrase. You may see it in:

• job applications
• public tenders
• official announcements
• enrollment procedures

So it can mean something like:

• expression of interest
• declaration of interest
• sometimes even application of interest, depending on context

It is more formal than everyday speech.

έγινε is:

• aorist tense
• 3rd person singular
• from the verb γίνομαι

Here it means something like:

• was done
• took place
• happened

Because the subject is singular (η εκδήλωση), the verb is also singular: έγινε.

Not in this sentence.

The verb γίνομαι can mean different things depending on context:

• become
• happen
• take place
• be done

Here, Η εκδήλωση ενδιαφέροντος έγινε ηλεκτρονικά means the expression of interest was done electronically or was submitted electronically, not became electronic.

So this is a good example of how γίνομαι is broader than English become.

Here ηλεκτρονικά is an adverb, meaning electronically.

It comes from the adjective:

• ηλεκτρονικός = electronic

Greek often uses the neuter plural form of an adjective as an adverb:

• κανονικός → κανονικά = normally
• φυσικός → φυσικά = naturally / of course
• ηλεκτρονικός → ηλεκτρονικά = electronically

So in this sentence, ηλεκτρονικά tells us how the action was done.

Yes, very often.

Strictly speaking, ηλεκτρονικά means electronically, but in modern official Greek it often implies:

• online
• through an electronic system
• via the internet

Depending on context, English might translate it as either electronically or online.

No, Greek word order is fairly flexible.

The original sentence:

• Η εκδήλωση ενδιαφέροντος έγινε ηλεκτρονικά.

is the most neutral and natural formal order.

You could also say:

• Ηλεκτρονικά έγινε η εκδήλωση ενδιαφέροντος.

This puts more emphasis on ηλεκτρονικά.

So the meaning stays basically the same, but the focus changes.

Yes, this is definitely formal / bureaucratic Greek.

A more everyday version would depend on the situation. For example:

• Δήλωσα ενδιαφέρον online. = I expressed interest online.
• Έκανα την αίτηση ηλεκτρονικά. = I made/submitted the application electronically.
• Το έστειλα online. = I sent it online.

So Η εκδήλωση ενδιαφέροντος έγινε ηλεκτρονικά sounds like something from an official notice, form, or announcement.

It is singular because the sentence is talking about the act/process of submitting an expression of interest, not necessarily about the number of people.

So singular can refer to:

• one specific submission
• one type of procedure
• the process in general

If you wanted the plural, you could say:

• Οι εκδηλώσεις ενδιαφέροντος έγιναν ηλεκτρονικά.
  = The expressions of interest were made electronically.

But in official language, the singular is often used for the procedure itself.

Here are the basic dictionary forms:

• η εκδήλωση = expression, declaration
• το ενδιαφέρον = interest
• γίνομαι = become, happen, be done
• ηλεκτρονικός, -ή, -ό = electronic

And the forms in the sentence are:

• η εκδήλωση = nominative singular
• ενδιαφέροντος = genitive singular
• έγινε = aorist, 3rd person singular
• ηλεκτρονικά = adverb

This is a useful sentence because it shows several very common patterns of formal Greek all at once.