my openWRT does not identify my modemstick, so i have to modify my openWRT
but i cannot do e.g. "opkg update" because of "failed establish connection"
i have a ubuntu-labtop connected to a WLAN-internet, the openWRT modem is connected to the labtop by LAN, the modem is NOT connected to internet, there is no WAN.
You need to establish some temporarily internet connection to download the required packages, which you then install on your router.
Perhaps, you can use a laptop/PC to connect your modem stick and connect to the Internet, assuming your laptop/PC already has the drivers installed? Otherwise, you may need to take your laptop out, find a public network, download the OpenWrt drivers (or source code), bring them back and install on your router.
Downloading http://downloads.openwrt.org/releases/19.07.3/targets/ramips/mt76x8/packages/Packages.gz
Failed to establish connection
*** Failed to download the package list from http://downloads.openwrt.org/releases/19.07.3/targets/ramips/mt76x8/packages/Packages.gz
Downloading http://downloads.openwrt.org/releases/19.07.3/targets/ramips/mt76x8/kmods/4.14.180-1-d92769dc5268e102503ae83fe968a56c/Packages.gz
Failed to establish connection
*** Failed to download the package list from http://downloads.openwrt.org/releases/19.07.3/targets/ramips/mt76x8/kmods/4.14.180-1-d92769dc5268e102503ae83fe968a56c/Packages.gz
then i download this *.gz-packages on my labtop, when i unpack the gz-files, i get files without ending
The gz-files are package lists, not packages. You don't need to update package lists on your router. You need to download *.ipk packages on your laptop, copy them over on your router, and install them.
Later, when you have your connection from router active, you can do opkg update and install more packages from the internet.
Be aware! You have to choose the correct release tree you are using on your device and the correct architecture/platform according to your router hardware.