OK, I have run into this as well. I still can’t get my old site to work but new sites now work after following some of the instructions here (Local doesn't open on Debian - #9 by 42Glider).
Firstly I checked if libcap2-bin was installed,
sudo apt-get install libcap2-bin
Then opened a terminal and changed to the Local directory,
cd /opt/Local
and changed the permissions of chrome-sandbox with,
sudo chmod 4755 chrome-sandbox
Finally I started Local and in preferences/advanced set the router mode to localhost. Created a new site and it works.
It’s a bit of a bad work around but at least you can play even if I wouldn’t really trust it. BTW, I also tried adding kernel.unprivileged_userns_clone = 1 to /etc/sysctl.conf and then reloading it but that didn’t solve anything further for me.