So even if I download a new launcher.jar manually and put it into data/, it gets  overwritten by a stale version on https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma.

When I make launcher.jar readonly the updater fails. I see no option to tell it to not update.

I am also trying the new launcher, but it does not start (see MCL-12329).

$ java -jar Minecraft.jar --workDir data
Bootstrap (v5)
Current time is Oct 16, 2019 9:37:27 PM
System.getProperty('os.name') == 'Linux'
System.getProperty('os.version') == '5.2.9-1-default'
System.getProperty('os.arch') == 'amd64'
System.getProperty('java.version') == '1.8.0_222'
System.getProperty('java.vendor') == 'IcedTea'
System.getProperty('sun.arch.data.model') == '64'

Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma
Got reply in: 1051ms
Downloaded 1076,7kb in 4s at 255,8kb/s
Renaming /home/ensonic/Minecraft/data/launcher.pack.lzma.new to /home/ensonic/Minecraft/data/launcher.pack.lzma
Renamed successfully.
Reversing LZMA on data/launcher.pack.lzma to /home/ensonic/Minecraft/data/launcher.pack
Unpacking /home/ensonic/Minecraft/data/launcher.pack to data/launcher.jar
Cleaning up /home/ensonic/Minecraft/data/launcher.pack
Starting launcher.
[21:37:36 INFO]: Minecraft Launcher 1.6.89-j (through bootstrap 5) started on linux...
[21:37:36 INFO]: Current time is Oct 16, 2019 9:37:36 PM
[21:37:36 INFO]: System.getProperty('os.name') == 'Linux'
[21:37:36 INFO]: System.getProperty('os.version') == '5.2.9-1-default'
[21:37:36 INFO]: System.getProperty('os.arch') == 'amd64'
[21:37:36 INFO]: System.getProperty('java.version') == '1.8.0_222'
[21:37:36 INFO]: System.getProperty('java.vendor') == 'IcedTea'
[21:37:36 INFO]: System.getProperty('sun.arch.data.model') == '64'