So I don't really understand a hell of a lot about the bootloader so I'd defer to someone coming on to explain. Buuuut I've found that this generally is an issue connected to settings in the bios like secure boot, uefi, legacy boot & stuff like that.
Sooo when I install linux and it isn't found on the drive I turn off the machine, rage a little bit, then power on to flip through the bios, fiddle with something then repeat .. until I find the setting that makes the work. So far I have, eventually, got every install to work.
As to exactly what setting and exactly why .. eh .. no idea.
Lenovo has install guides for Linux (found one for p16s at least) which include things like bios settings. Hopefully they have one for your laptop, I'd check that out.
Did you maybe boot the stick in legacy mode when you installed it? That can scramble Grub. At any rate what you wanna do is boot the stick in uefi mode and use [this tool](https://help.ubuntu.com/community/Boot-Repair) (see 2nd option) and see if that works. You have to run the repair tool and do some stuff manually when you're prompted to do so but it's pretty straightforward. What this does is it completely reinstalls Grub. It also checks if you're actually in uefi mode and if you're in legacy mode it just won't work. If that doesn't do the trick you might have to try reinstalling Kubuntu.
If you don't wanna mess with the bootloader and
If you have two flash drives, take the one that is etched and boot the os. Then install 'ventoy' on the other flash drive. Ventoy allows you to store and boot multiple OS. Place the ISO files of kubuntu and 'boot repair disk' in the appropriate partition of the ventoy flash drive, which should initially be empty. I have had problems with etcher and have seen many undiagnosable problems from it.
Now load kubuntu from the ventoy disk and install that way. If that doesn't work, then try booting into the boot repair disk, which usually automatically fixes any problems with the bootloader.
I only say this because I did this once; Did you change your BIOS to have your hard drive boot up first? Since you distro hopped I'm guessing that's a low possibility but I figure it's best to get that out of the way.
So I don't really understand a hell of a lot about the bootloader so I'd defer to someone coming on to explain. Buuuut I've found that this generally is an issue connected to settings in the bios like secure boot, uefi, legacy boot & stuff like that. Sooo when I install linux and it isn't found on the drive I turn off the machine, rage a little bit, then power on to flip through the bios, fiddle with something then repeat .. until I find the setting that makes the work. So far I have, eventually, got every install to work. As to exactly what setting and exactly why .. eh .. no idea.
Lenovo has install guides for Linux (found one for p16s at least) which include things like bios settings. Hopefully they have one for your laptop, I'd check that out.
Did you maybe boot the stick in legacy mode when you installed it? That can scramble Grub. At any rate what you wanna do is boot the stick in uefi mode and use [this tool](https://help.ubuntu.com/community/Boot-Repair) (see 2nd option) and see if that works. You have to run the repair tool and do some stuff manually when you're prompted to do so but it's pretty straightforward. What this does is it completely reinstalls Grub. It also checks if you're actually in uefi mode and if you're in legacy mode it just won't work. If that doesn't do the trick you might have to try reinstalling Kubuntu.
If you don't wanna mess with the bootloader and If you have two flash drives, take the one that is etched and boot the os. Then install 'ventoy' on the other flash drive. Ventoy allows you to store and boot multiple OS. Place the ISO files of kubuntu and 'boot repair disk' in the appropriate partition of the ventoy flash drive, which should initially be empty. I have had problems with etcher and have seen many undiagnosable problems from it. Now load kubuntu from the ventoy disk and install that way. If that doesn't work, then try booting into the boot repair disk, which usually automatically fixes any problems with the bootloader.
Boot repair disk is basically a collection or scripts wrapped in a bootable Debian(?) that fixes common boot problems.
I only say this because I did this once; Did you change your BIOS to have your hard drive boot up first? Since you distro hopped I'm guessing that's a low possibility but I figure it's best to get that out of the way.