To add to that, try to download a recent ISO of Manjaro (Download x86 – Manjaro) before reinstalling. Kernel 5.15.78 became outdated in November 2022 (Index of /pub/linux/kernel/v5.x/), so if you are trying to fix and/or reinstall the system using a 2 year old ISO, then you will encounter a huge number of problems. There have been many changes to Manjaro since then and updating from an old ISO or unmaintained installation will result in a lot of software conflicts and changes to configuration files which will definitely require manual intervention.
Also, I hope that you have learned your lesson about using AI to try to solve problems that require human thinking and decision-making. Advice from AI seems to be the fastest, most reliable way to turn a working system into a broken system. The best advice can always be found here, on this forum, where people who have been using Manjaro for many years are always eager to provide guidance and help sort out even the most intractable of system issues.
Finally, this might be worth a read for you (and your brother, as you said that it is his system, and the very old kernel appears to indicate that it has not been properly updated/maintained for nearly 2 years):