Is the traffic missing in MSFS today? I see no other planes at airports I'm flying from or arriving at. Did I miss some news on this?

Yes, no traffic at EGLL at the moment. Better to use FSLTL Traffic Injector (with either Navigraph or RealTraffic) as they seem to be more stable.

Edited June 23Jun 23 by rksoftware

I'd treat it as a live/default traffic issue first, not necessarily something you changed locally. When the sim's own online traffic goes quiet it can look exactly like that at otherwise busy airports.

For that reason I usually keep an injector option around for offline flying. FSLTL is a good quick check, and AIG is still useful if you care about model and schedule coverage. If those inject traffic normally while the default/live option is empty, that points more to the sim service or data side than your install.