I installed syncthing 1.9 on Ubuntu 20.4 LTS in accordance with the instructions on the syncthing website. The install went well, no errors but I have no GUI. In a term window syncthing responds to “synthing -version” with:
syncthing v1.9.0 “Fermium Flea” (go1.15.1 linux-amd64) deb@build.syncthing.net 2020-08-28 05:48:25 UTC [noupgrade]
But I cannot access the GUI with Firefox.
Can you check the command line output (or the logfile, if enabled) and look for a line similar to [XXXXX] 00:00:00 INFO: GUI and API listening on 127.0.0.1:8384? Is the port actually 8384? Syncthing will use a different one if 8384 is already in use.