It refers to an invalid NBT entry "Muskellunge" - if this is a player, backup and delete the playerdata file (check the playerdata folder in your worldsave)
Did you check the bin folder?
Maybe also make a test with another Java build like Azul Zulu
https://www.azul.com/downloads/?version=java-17-lts&os=windows&architecture=x86-64-bit&package=jre#zulu
The path is something like:
C:\Program Files\Zulu\zulu-17\bin\javaw.exe
Yes - Update 6 makes larger changes which is breaking these addons
Most addons already have the update - some are still in the update process and will be released in the next days
Check the PC for the Java 17 installation
The Oracle Java default path is
C:\Program Files\Java\jdk-17\bin\javaw.exe
Open the bat file and replace the world java with the path and put it into quotation marks
"C:\Program Files\Java\jdk-17\bin\javaw.exe" -Xmx4G -jar server.jar
pause
Make sure the java path is correct - the server jar file name also have to match
Some Create addons are not compatible with the Create 6 update
Like Create Big Cannons, Create Confectionery or Create Steam N Rails and maybe more
You have to wait for these updates - or just remove the addons