Using hostnamectl is a good start, but also check your network configuration on your router - sometimes raspbian will pick up the hostname that it reported to the router when it was first assigned an IP address. Most routers drop this table when they reboot, so rebooting your router could be the easiest fix.
One good option is to create a static DHCP entry ...
First, like @Milliways said, check that your SD card is still OK. Create a file, reboot, and verify that the file is still there. Or try using the script @Ingo wrote.
If your SD card is writable, you might want to try setting the hostname the Debian way:
sudo hostnamectl set-hostname my_name
raspi-config is a bash script.
It has NO settings, it is just a front end to the many config files.
You can read the script to see what it does, although it is rather long and involved.
If you asked a more specific question about what settings you are interested in you may be able to get more details.
This is an exercise in futility.
Raspi-config is a simple (if long) bash script to configure Raspberry Pi OS.
Ubuntu has a different structure (so even though it shares some files they are located in different places), it uses different networking and has a different kernel.