It works for me (on 5.18.11-200.fc36.x86_64).

Please, copy & past output from LOOPDEV_DEBUG=all losetup /dev/loop5 /dev/sdc -b 4096 -P

at first Thanks for answer!!!

Here the output:
root@arm_pc:/home/user# losetup /dev/loop5 /dev/sdd -b 4096 -P
14907: loopdev: CXT: [0xbec437e0]: initialize context
14907: loopdev: CXT: [0xbec437e0]: init: ignore ioctls
14907: loopdev: CXT: [0xbec437e0]: init: loop-control detected
14907: loopdev: CXT: [0xbec437e0]: /dev/loop5 name assigned
14907: loopdev: CXT: [0xbec437e0]: add_device 5
14907: loopdev: CXT: [0xbec437e0]: add_device done [rc=-1]
14907: loopdev: CXT: [0xbec437e0]: set flags=8
14907: loopdev: CXT: [0xbec437e0]: set blocksize=4096
14907: loopdev: CXT: [0xbec437e0]: set backing file=/dev/sdd
14907: loopdev: SETUP: [0xbec437e0]: device setup requested
14907: loopdev: SETUP: [0xbec437e0]: backing file open: OK
14907: loopdev: CXT: [0xbec437e0]: open /dev/loop5 [rw]: Success
14907: loopdev: SETUP: [0xbec437e0]: device open: OK
14907: loopdev: SETUP: [0xbec437e0]: LOOP_SET_FD: OK
14907: loopdev: SETUP: [0xbec437e0]: calling LOOP_SET_BLOCK_SIZE
14907: loopdev: CXT: [0xbec437e0]: LOOP_SET_BLOCK_SIZE failed: Invalid argument
14907: loopdev: SETUP: [0xbec437e0]: failed [rc=-22]
losetup: /dev/sdd: failed to set up loop device: Invalid argument
14907: loopdev: CXT: [0xbec437e0]: de-initialize
14907: loopdev: CXT: [0xbec437e0]: closing old open fd
14907: loopdev: ITER: [0xbec439b8]: de-initialize

Btw how did you do that with the environment var set and then disassemble the code lines inside of the progam. An internal LDE (Sorry, I am just stuck in ancient development methods : { and in case of the problem: Is there any way to get around e.g.. by blockdev did not work) Thanks in advance

It seems like the old version of util-linux (2.36 or so), right? The latest versions use LOOP_CONFIGURE ioctl to configure all in one step.

Anyway, I'm not sure where the problem is. It seems losetup does it right; maybe the old kernel has not backported all necessary patches to work with loop device blocksize properly. You can also try strace to see more details about the syscalls.

Ad debugging, it's pretty simple, LOOPDEV_DEBUG=all activates debug messages (just printf() calls) in the code.

Thanks. No, I downloaded the util-linux here last week from this site. As far to mention to the kernel it is a newer one (uname-r) but the kernel is specific for the ARM machine by the vendor. That's bad... Anyway thanks