Die Siegbedingung gilt, doch die Punkteleiste fehlt.

Because both Siegbedingung and Punkteleiste are feminine singular nouns.

• die Siegbedingung
• die Punkteleiste

In German, the article must match the noun’s gender, number, and case. Here, both nouns are feminine and singular.

Both are in the nominative case because each one is the subject of its own clause.

• Die Siegbedingung gilt
• die Punkteleiste fehlt

A useful way to see this is:

• What gilt? → die Siegbedingung
• What fehlt? → die Punkteleiste

So both are subjects, and subjects are usually nominative.

Gilt is the 3rd person singular present form of gelten.

In this sentence, gelten means something like:

• to be valid
• to apply
• to be in effect

So Die Siegbedingung gilt means that the victory condition is recognized as valid or applies in this situation.

Also note the verb form:

• ich gelte
• du giltst
• er/sie/es gilt

It is a strong verb, so the stem vowel changes in the er/sie/es form.

Both can be possible in some contexts, but they are not always identical in tone or usage.

• Die Siegbedingung gilt = the victory condition applies / is in force
• Die Siegbedingung ist gültig = the victory condition is valid

gelten often sounds more natural when talking about a rule, condition, law, or principle that is currently in effect.
So here, gilt is a very idiomatic choice.

Here doch means but / however.

So:

• ..., doch die Punkteleiste fehlt.
• ..., aber die Punkteleiste fehlt.

Both are possible.

The difference is mostly one of style and nuance:

• aber is the most common everyday word for but
• doch can sound a little more formal, literary, or pointed
• doch often highlights a contrast a bit more strongly

So the sentence with doch feels slightly more polished or emphatic.

Because doch is connecting two main clauses:

1. Die Siegbedingung gilt
2. doch die Punkteleiste fehlt

In German, when two independent clauses are linked by conjunctions like aber, doch, denn, oder, and so on, a comma is normally used.

So the comma is standard here.

It is not really being moved to the end by a special rule; it is simply in the normal main-clause verb-second position.

The second clause is:

• die Punkteleiste fehlt

That has:

1. subject: die Punkteleiste
2. finite verb: fehlt

In a German main clause, the finite verb usually comes in second position. Since the clause is short and nothing comes after the verb, the verb also happens to be the last word.

Compare:

• Die Punkteleiste fehlt.
• Die Punkteleiste fehlt noch.
• Die Punkteleiste fehlt im Menü.

The verb is still in second position, even when it is not the last word.

They are both compound nouns, which are very common in German.

Siegbedingung

• Sieg = victory
• Bedingung = condition

So literally: victory-condition

Punkteleiste

• Punkte = points
• Leiste = bar / strip / panel

So literally: points-bar or score bar

A very important rule for German compounds:
the last part determines the gender and the basic grammatical behavior.

• die Bedingung → therefore die Siegbedingung
• die Leiste → therefore die Punkteleiste

Because in German, all nouns are capitalized, not just proper names.

So:

• die Siegbedingung
• die Punkteleiste

This is completely normal German spelling. Adjectives, verbs, and conjunctions are usually not capitalized unless they begin the sentence.

Yes, German allows some flexibility, though not every version sounds equally natural.

For example, you could say:

• Die Siegbedingung gilt, doch die Punkteleiste fehlt.
• Doch die Punkteleiste fehlt.
• Die Punkteleiste fehlt, doch die Siegbedingung gilt.

You could also front another element for emphasis in a larger context. But in each main clause, the finite verb still follows the normal verb-second rule.

So the original sentence is a straightforward, natural version.