So issue started after the July 1 updates?
Or after the updates yesterday, involved these packages:
[2020-07-03T08:47:03-0500] [ALPM] upgraded popt (1.16-10 -> 1.18-11)
[2020-07-03T08:47:03-0500] [ALPM] upgraded imagemagick (6.9.11.20-1 -> 6.9.11.22-1)
[2020-07-03T08:47:03-0500] [ALPM] upgraded nspr (4.25-1 -> 4.26-1)
[2020-07-03T08:47:03-0500] [ALPM] upgraded libva (2.7.1-1 -> 2.8.0-1)
[2020-07-03T08:47:04-0500] [ALPM] upgraded nss (3.53.1-1 -> 3.54-1)
[2020-07-03T08:47:04-0500] [ALPM] upgraded croeso (1.3-1 -> 1.4-1)
[2020-07-03T08:47:13-0500] [ALPM] upgraded python3-idna (2.9-1 -> 2.10-1)
[2020-07-03T08:47:13-0500] [ALPM] upgraded unrar (5.9.3-1 -> 5.9.4-1)
If it started after July 1, then it probably is new mesa. For July 3, if that update broke iCloud access in QtWebengine, then it probably is nss/nspr.
Start Falkon from cli (either yakuake or konsole, type falkon
to run) and post the output from cli after it crashes.
Even better would be to run in gdb, but then you need to install debug packages for it to be useful, so let's hope just running from cli will give a clue.