Thanks, it was pretty easy after all:
Edit /etc/opkg/distfeeds.conf
changing the URLs from https to http
opkg install libopenssl
opkg install openssl-util
opkg --force-depends remove libustream-wolfssl20201210
opkg install libustream-openssl20201210
Edit /etc/opkg/distfeeds.conf
changing the URLs back to https
opkg update
now works
service uhttpd restart