Exit Code 1 appears after many different failures. Open the log for the affected installation as soon as it closes. Another launch can replace latest.log.
Find the installation’s game directory
Check the game directory in the launcher profile. Look for these paths inside it. If there is no crash report, inspect the first relevant ERROR or Caused by entry before shutdown in latest.log.
logs/latest.log
crash-reports/
Create a separate, clean installation of the same Minecraft version. If it starts, add the loader and then mods in small groups. If the clean profile also fails, follow the Java, graphics or file-access error in the report.
Change one variable per attempt. Use a separate game directory so the test can leave your existing worlds and settings intact.