Mikrotik hap ac3 OS7.2

I recently buy a brand new Mikrotik hap ac3. the problem is, the routerOS current version is 7.2 that no compatible with Openwrt. beside of that, there is no way to downgrade the current firmware to 6.
Is there any solution for this problem?

any suggestion?

Have you tried installing and booting the OpenWrt image normally (from NAND/UBI)?
Make sure you save a full dump of the NOR & NAND before you install.

I think I remember when I tried an early v7 RouterBOOT with my RB450gx4, it did boot. The yaffs devices (NOR only, or non-ipq40xx) are another story.