Hi, I am having this issue regarding missing blocks. I am running it on raspberry pi 4 with GNU Radio version 3.7. I followed your steps but I am not able to resolve this issue.
The terminal output is as follows

(my_root)raspi@raspi:~/gr-adsb/examples $ gnuradio-companion adsb_rx.grc
<<< Welcome to GNU Radio Companion 3.7.13.4 >>>

Block paths:
/usr/share/gnuradio/grc/blocks

Loading: "/home/raspi/gr-adsb/examples/adsb_rx.grc"
Block key "adsb_decoder" not found
Block key "adsb_demod" not found
Block key "adsb_framer" not found
Block key "sqlite_sink" not found

Done