I was starting up 1.15.2 with java.exe and this happened.
[08:00:23 INFO]: Job 'Resources' finished successfully (took 0:01:56.169)
[08:00:23 INFO]: Launching game
[08:00:23 INFO]: Unpacking natives to C:\Users\Ty hartman\AppData\Roaming\.minecraft\versions\1.15.2\1.15.2-natives-340039958541700
[08:00:23 INFO]: Launching in C:\Users\Ty hartman\AppData\Roaming\.minecraft
java.lang.RuntimeException: Classpath file not found: C:\Users\Ty hartman\AppData\Roaming\.minecraft\ms-starter.jar
at net.minecraft.launcher.game.MinecraftGameRunner.constructClassPath(MinecraftGameRunner.java:396) ~[launcher_mcpatched.jar:1.6.89-j]
at net.minecraft.launcher.game.MinecraftGameRunner.createArgumentsSubstitutor(MinecraftGameRunner.java:300) ~[launcher_mcpatched.jar:1.6.89-j]
at net.minecraft.launcher.game.MinecraftGameRunner.launchGame(MinecraftGameRunner.java:169) ~[launcher_mcpatched.jar:1.6.89-j]
at com.mojang.launcher.game.runner.AbstractGameRunner.onDownloadJobFinished(AbstractGameRunner.java:186) [launcher_mcpatched.jar:1.6.89-j]
at com.mojang.launcher.updater.download.DownloadJob.popAndDownload(DownloadJob.java:122) [launcher_mcpatched.jar:1.6.89-j]
at com.mojang.launcher.updater.download.DownloadJob.access$000(DownloadJob.java:12) [launcher_mcpatched.jar:1.6.89-j]
at com.mojang.launcher.updater.download.DownloadJob$1.run(DownloadJob.java:86) [launcher_mcpatched.jar:1.6.89-j]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_251]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_251]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_251]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_251]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_251]
I got the same thing when I used javaw.exe. These logs are from the launcher.
There is no debug.txt to be found.