Your questions show (no offence intended ) that you miss at tthe moment a general understanding of the matter.
The first absolute sector of a storage device (LBA 0 or CHS 0/0/1) normally contains either of:
1) a MBR (Master Boot Record) and if in this MBR there is at least one valid entry in the partition table the device is a partitioned device
2) a PBR or VBR (Partition Boot Record or Volume Boot Record) and if in this PBR/VBR there are valid values in the BPB (Bios Parameter Block) the device is non-partitioned or - commonly - a "super-floppy"
BUT it is entirely possible that *anything* else is written to it.
A MBR is defined as follows:
1) the boot code, some assembly code from byte offset 0 to byte 439 (that can well be all 00's)
2) the Disk Signature (on NT Systems) 4 bytes that can well be all 00's starting at offset 440
3) the partition table, 4 entries, 16 bytes each, starting at offset 446
4) the Magic Bytes (the hex values 55 AA) at offset 510
A PBR or VBR is defined as follows:
1) three "jump bytes" usually, but not always, EB xx 90 allowing to jump over the BPB
2) the BPB (that varies between different file systems bith in contents/fields AND in length)
3) some boot code, starting from the end of the BPB and up to offset 509
4) the Magic Bytes (the hex values 55 AA) at offset 510
Any OS might (or might not) use some (or some other) parameters to determine whether the sector is a MBR or a PBR, and decide to read/interpret (or fail to read/interpreter) the data in the partition table or in the BPB along the standards or not.
As well, any tool running under this (or that) OS may require (or not require) additional parameters (or various values in given fields) to decide whether what follows is a partitioned device or a volume and if it is a valid one.
The BIOS (generically speaking, as there are exceptions) usually does two things:
1) verify that the Magic Bytes (55 AA at offset 510) are present
2) execute the assembly code starting at offset 0 in the sector, no other questions asked
The net result of all the above is that it is perfectly possible to have a bootable device that is not accessible/readable by a number of OS (except for the booted from that device one) or that it is inaccessible/unreadable with this (or that) tool.
Since all the info/parameters that may affect the way a given OS (or given tool) behaviour reside on this first sector of the device, the "universal" way to have the device (unpartitioned and unformatted) readable/accessible by *any* OS is to simply fill this sector with 00's.
This can be done by *any* hex/disk editor or by dd (or similar tool that can access the \\.\PhysicalDrive under Windows).
Once the first sector is 00'ed (possibly an unmount-mount, or reboot is needed to be able to access the device in its 00ed status, this depends on the specific OS and on the specific tool) for all that matters the device is in its "factory state", i.e. when connected to a NT based systyem, it will show as "this device needs to be initialized" in Disk Manager.
Gparted is a very good (but a tad bit too smart for its own good) tool as it attempts to read/interpret the contents of the MBR and PBR's/VBR's and if it finds something that is not "standard" (it's own standard, which is almost - but not quite - the actual standard, only as an example it has - or had - issues with FAT12 volumes on partitioned media, recognizes .iso partitions but can't do anything with them, etc.) .
Every other "smart" tool will have this (or that) peculiar way to deal with anything that is not EXACTLY "canonical" (and often have also some quirks with something that is actually correct or at least doable and not affecting anything in the OS), BalenaEtcher very likely expects this first sector to be either 00's (uninitialized) or to contain "valid" values, and throws a fit if neither of these two conditions are met.
For *whatever* reasons your checkn1x, once copied to a USB stick produces something that works (i.e. boots and works as expectred) BUT that is *somehow* non-standard.
Like many other tools both Gparted and BalenaEtcher belong to the category of "if it works, it works just fine, when it doesn't work, it doesn't work and you will likely never know why exactly" programs.
Use - when they don't work - other tools, possibly less "smart" and more "direct".
Wonko