I change it as you say:

dest root /
dest ram /tmp
lists_dir ext /var/opkg-lists
option overlay_root /dev/sdb1

and i try

option overlay_root /tmp/mountd/disk1_part1

My mount point, usb flash with /overlay is /tmp/mountd/disk1_part1 |18.71 GiB / 19.90 GiB

But have same errors with both variant

root@GL-AX1800:~# opkg list-upgradable
zerotier - 1.8.4-1 - 1.8.4-2
Collected errors:
 * pkg_get_installed_files: Failed to open //usr/lib/opkg/info/gl-sdk4-mwan3.list: No such file or directory.
 * pkg_get_installed_files: Failed to open //usr/lib/opkg/info/kmod-crypto-manager.list: No such file or directory.
 * pkg_get_installed_files: Failed to open //usr/lib/opkg/info/kmod-crypto-pcompress.list: No such file or directory.
 * pkg_get_installed_files: Failed to open //usr/lib/opkg/info/python3-urllib.list: No such file or dire