@mkouba you can install pre-release of vscode-quarkus:

to test Qute debugger, you need to do some (boring) configuration:

get the PR from Quarkus Provide Qute DAP debugger support quarkusio/quarkus#48962
build Quarkus https://github.com/quarkusio/quarkus/blob/main/CONTRIBUTING.md#building-main or only Qute artifacts that you need (see pom.xml with dependencies that you will to do in the previous comment)
Create or open a Qute project
Add in the pom.xml of the Qute project

        <dependency>
            <groupId>io.quarkus.qute</groupId>
            <artifactId>qute-core</artifactId>
            <version>999-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>io.quarkus.qute</groupId>
            <artifactId>qute-debug</artifactId>
            <version>999-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>io.quarkus</groupId>
            <artifactId>quarkus-qute</artifactId>
            <version>999-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>io.quarkus</groupId>
            <artifactId>quarkus-qute-deployment</artifactId>
            <version>999-SNAPSHOT</version>
        </dependency>

add in the .vscode/launch.json the Qute attach debugger which will start the Qute debugger on 4711 port:

{
    "version": "0.2.0",
    "configurations": [
...
        {
            "type": "qute",
            "request": "attach",
            "name": "Attach to Qute Debugger",
            "port": 4711
        }
    ]
}

update .vscode/tasks.json to set the Qute debug port

"command": "./mvnw quarkus:dev -DquteDebugPort=4711",
"windows": {
	"command": ".\\mvnw.cmd quarkus:dev -DquteDebugPort=4711"
}

set a breakpoint to a Qute template
start the Quarkus application (like before)

Wait for that Qute debugger is started by the Quarkus app. You should see trace like:

__  ____  __  _____   ___  __ ____  ______ 
 --/ __ \/ / / / _ | / _ \/ //_/ / / / __/
 -/ /_/ / /_/ / __ |/ , _/ ,< / /_/ /\ \
--\___\_\____/_/ |_/_/|_/_/|_|\____/___/
2025-08-12 21:08:37,566 INFO  [io.qua.roq.plu.asc.run.AsciidoctorJConverter] (Quarkus Main Thread) Starting Asciidoctorj...

2025-08-12 21:08:50,522 INFO  [io.qua.roq.plu.asc.run.AsciidoctorJConverter] (Quarkus Main Thread) Asciidoctorj started in 12952ms
DebugServerAdapter listening on port 4711
Waiting for a new DAP client...