It is likely that this package is dependent on the current version of openwrt (19) which gl-inet is still unable to adapt to the gl-ar750s (still stuck on 18).
You may be able to just build the new package yourself for openwrt 18.
Otherwise, your best bet is to pray that gl-inet will get around to updating the gl-ar750s to openwrt 19 one day if you want the new package.
Otherwise, gl-inet may eventually officially release the adguard home software for the gl-ar750s which will have similar features to the adblock package and will not depend on openwrt 19.