after upgrading to 21.02 there are some issues with opkg. Firstly, all kernel module packages where missing. I manually had to add src/gz openwrt_kmod https://downloads.openwrt.org/releases/21.02.0/targets/ath79/generic/kmods/5.4.143-1-79c5dc6db69102eb2943a96b9bec8b63/ to get them working.
Secondly I cannot install librt (as a dependency of usb-modeswitch), the package is missing in the repo. For snapshot it's available. There's also no faillog for this package. Did I miss something? What can I do to get this package installable?