Your password cannot change itself.
Can you login via TTY?
It may be that you’re experiencing some latency in the SDDM login window, and keys you press skip or similar. You could try typing your password (very) slowly; or wait until SDDM has loaded completely.
(Random ideas)
That kernel has reached EOL already.
Do yourself a favour, and always download the latest full Manjaro ISO.
Please provide system information;
the output of the following command:
inxi --admin --verbosity=8 --filter --no-host --width
Hi @noobToLinux and welcome to the Manjaro community.
As a new user, please take some time to familiarise yourself with Forum requirements; in particular, the many ways to use the forum to your benefit. To that end, some or all these links will be invaluable:
- [How to] Request Support
- [How to] Find Error Logs
- [How to] Find System Information
- [How to] Post Command Output and File Content as Formatted Text
- Forum Rules
- Strict Forum Rules and Guidelines
Last, but not least, the Stable Update Announcements, which you should check frequently for important update related information.
Cheers.