It’s awesome!!! Thank you very very much. It works perfectly.
Since I use both CalendarExt3 and CalendarExt3 Agenda, I have stored the key lines and if lines in both modules in the config.

For all-day events, the symbols are displayed in the calendar, but not in the agenda. And only for all-day events. But I don’t care. I’m happy.
Just in case you want to make an improvement here or I have made a mistake!!!

So thank you very much. I will post my project soon in the forum under “Show my Mirror” incl. all information from the config and custom.
Maybe someone will be interested… :-)

Original. (All these test events are from the same calendar)

eventTransformer: (ev) => {
	if (ev.title.search('Fitness') !== -1) {
		ev.symbol = [ 'fa-solid fa-dumbbell' ]
		if (!ev.isFullday) ev.title = ev.title.replace('Fitness', '<font color="pink">Fitness</font>')
	}
	return ev
}

After.

This is how I stored it in Config.js

		{
			module: "MMM-CalendarExt3",
			position: "bottom_bar",
			title: "Kalender",
			config: {
				mode: "week",
				useSymbol: true,
				eventTransformer: (ev) => {
						const customEvents = [
							{ keyword: "Gelber Sack", symbol: ["fa-solid fa-arrows-spin"], color: "yellow" },
							{ keyword: "Hausmüll", symbol: ["fa-regular fa-trash-can"], color: "green" },
							{ keyword: "Fitness", symbol: ["fa-solid fa-dumbbell"], color: "pink" },
						]
						const found = customEvents.find((condition) => {
							return ev.title.search(condition.keyword) !== -1
						})
						if (found) {
								ev.icon = [ found.symbol ]
								ev.color = found.color
						}
						return ev
				},
			}
		},

result

The all-day events are yellow and green.
I can understand the colorful font, but then I’ll see how I can get it into the .CX3. Can you do it there only for the keywords or only completely? I just want Fitness to be pink but everything else to stay black or white.

Unfortunately, the desired symbols are still not displayed.
They still remain at "arrow-right as I set it in the module: “Calendar”.
I have tried it in the config with [] and also without. Both here the same result.

I’ll try the “replace” later. Thank you! :-)

if I use ev.sybol = ‘trash-can’ my calendar module is no longer displayed, but if I use ev.symbol = [‘trash-can’] the entry is displayed without a symbol.

Broadcasted events information from default calendar module is not so well-formed. You should use like this.

["fa-solid fa-trash-can"]

I’m not sure somebody fix this issue, I reported long days ago. Anyway, until fix, use that way.

for “Fitness” I have selected the color “pink”. However, the “Fitness” entry is not colored pink, only the symbol. How do I make the font pink?

That was my intention. (I hate colored text. :D)

If you really want colored text, append belows into your css/custom.css

/* custom.css */
.CX3 .event.singleday .headline .title {
  color: var(--calendarColor);
}

If I abbreviate a birthday with “Geb.” and want to see the “birthday-cake” symbol instead of “Geb.”, how would I have to execute the “Replace” entry?

Maybe this… (not tested)

...
if (ev.title.search('Geb.') !== -1) {
  ev.title = ev.title.replace('Geb.', '')
  ev.symbol = ["fas fa-birthday-cake"]
}
...

{
	module: "MMM-CalendarExt3",
	position: "bottom_bar",
	config: {
		... // other configs...
		eventTransformer: (ev) => {
			const customEvents = [
				{ keyword: "Gelber Sack", symbol: "fas fa-arrows-spin", color: "yellow" },
				{ keyword: "Hausmüll", symbol: "fas fa-trash-can", color: "green" },
			]
			const found = customEvents.find((condition) => {
				return ev.title.search(condition.keyword) !== -1
			})
			if (found) {
				ev.icon = [ found.symbol ]
				ev.color = found.color
			}
			return ev
		},
	}
},

PS. It was a somewhat late answer. For your new questions, I’ll reply again.

My Config.js now looks like this

eventTransformer: (ev) => {
				if (ev.title.search("Gelber Sack") > -1) ev.color = 'yellow' 
				if (ev.title.search("Gelber Sack") > -1) ev.symbol = ['trash-can']
				if (ev.title.search("Blaue Tonne") > -1) ev.color = 'blue'
				if (ev.title.search("Fitness") > -1) ev.color = 'pink' 
				return ev
				}

But now I get the following result

The following problems occur.

1. all-day event such as “Gelber Sack” is well colored yellow. Everything is fine.
2. if I use ev.sybol = ‘trash-can’ my calendar module is no longer displayed, but if I use ev.symbol = [‘trash-can’] the entry is displayed without a symbol.
3. for “Fitness” I have selected the color “pink”. However, the “Fitness” entry is not colored pink, only the symbol. How do I make the font pink?

And finally, one more question:

If I abbreviate a birthday with “Geb.” and want to see the “birthday-cake” symbol instead of “Geb.”, how would I have to execute the “Replace” entry?

in Ext3 is a function instead of a black of values

eventTransformer: (ev) => {
  if (ev.title.search("Gelber Sack") > -1) ev.color = 'yellow'  // you would need a line like this for each color thing u want to change
// and symbol
  return ev
}

						customEvents: [{keyword: "Gelber Sack", symbol: "arrow-spin", color: "yellow"},
						{keyword: "Hausmüll", symbol: "trash-can", color: "green"}],

effectively the same code as in the default calendar. check the subject and set the color and symbol if you want different than what calendar sends

calendar sends the hard coded values from config.js.

Of course it is a normal standard entry if you are familiar with the language, but I am just trying to learn everything on my own, but I still need a lot of information and occasionally need to be told how the whole thing works

Can you perhaps create an example entry for the Custom.css or show me what the entry should look like so that I get the entries in CalendarExt3 and Agenda as shown in the following picture?
So that I can assign a color to a specific keyword and also create a separate symbol for the keyword?

And the whole thing for several keywords that you want to color differently and provide with a symbol?

The screenshot is from the standard calendar, but I would like to be able to enter the entries in your calendar @MMRIZE in exactly the same way.

Or you can use eventTransformer feature of CX3. For that kind of inconvenience, I prepared that feature in CX3. Read the README.

BUT ext3 has filters too, so you can do it over there…