Which version? (snapshot/master, 18.06.x, old v17, ancient)?
Did you successfully run
opkg update
before trying opkg list?
(Using the pre-format button </> above to make commands and output more readable)
https://openwrt.org/toh/netgear/wgt634u is a 200 MHz, Broadcom BCM5365 SoC with 32 MB of RAM. Your results with that SoC and real-time audio are likely to be less than stellar.
Archer C7 is a different SoC architecture, so the packages for it may be different.