Capitalized adjectives after indefinite words
In English, when you want to describe an undefined thing, you simply put an adjective after a word like something or nothing. You might say something new or nothing important. In German, this works a bit differently.
After indefinite words like etwas or nichts, the adjective actually transforms into a neuter noun. Because it acts as a noun, you must capitalize it. It also needs a specific grammatical ending. This can feel unnatural at first because English adjectives never change their forms or turn into nouns in this exact way.
Most indefinite words force the adjective that follows to take the strong neuter ending -es. This group includes etwas, irgendetwas, and nichts. It also includes basic quantity words like viel and wenig. The capitalized adjective then acts as the noun of the phrase.
You will also see this exact same -es pattern after longer phrases and other words that express quantity. Words like mehr and genug, as well as phrases like ein bisschen, ein wenig, or zu viel, all call for the capitalized adjective with an -es ending.
There is one very important exception to the -es rule. When you use the word alles, the capitalized adjective takes the weak ending -e instead.
This happens because alles already shows a strong ending itself, so the adjective does not need to do the heavy grammatical lifting. This is part of the standard adjective ending rules, a principle you might recognize from when adjectives are turned into nouns for people.
When you describe indefinite concepts in German, the adjective becomes a capitalized neuter noun. Most of the time, such as after etwas, nichts, viel, or quantity phrases, you add -es to the adjective. However, when you use alles, the ending changes to a simple -e.