Zend certified PHP/Magento developer

Boot Windows (7,10,11) installation in GRUB on GPT partittioned USB

The question is why chainloader +1 works with MBR partittioned USB and can boot with bootmgr but GPT version of my USB stick brings me back to GRUB console after chainloading? Also no luck with ntldr /bootmgr command. PC runs in legacy mode (BIOS). devicemap and parttool doesn’t provide its functionality for GPT.