Mine was like this even prior to the update. Career Mode has always run well, 50-70fps on Medium/High settings so there is something else going on.
Last night I spawned at KLAX and was getting 12fps and the GPU usage was at 100%, drawing around 150W (normally other titles draw 280-320W at the same GPU usage including MSFS2020). Even quitting back to the menu, the fps never recovered. I respawned at KLAX and was playing around with the settings randomly, toggling the on and off and out of nowhere the performance shot back up to 60-65fps which is more what I was expecting, power draw went up to 315W (also what I would expect for 100% usage), there is some weird GPU/VRAM utilisation going on.
I should also add that MSI Afterburner/RTSS shows I was using 7.5GB VRAM out of 10GB, but DevMode showed >9GB/9GB in red for VRAM use.
Happy to get any further details, screenshots, etc to assist with fault finding.