HVAC fan turned off by itself with associated burning smell
Your fan was not running and a hot smell points to a thermal overload in your fan motor tripping.
Why would this happen? The lubricant in the motor has dried out and the bearings are getting stiff if a belt drive it could also include the bearings on the fan itself.
Can it be fixed: Usually yes
The fan motor usually has ports over the ends that lead to the bearings. I use 30 weight motor oil but any motor oil will usually help.
Most motors only take about 20 drops of oil if the tube or shaft fills up run the motor for a while and check it later,  if you can get 10-20 Drops in let it run and the problem may go away for a year or longer but adding a few drops every 6 months can extend the motor life by decades.
The reason the motor was not running it overloaded due to lack of lubricant and there is a thermal snap switch in the motor that had not cooled down yet. I have done this little trick hundreds of times and brought motors back to life.
Don’t forget to wash your grids I can’t believe how bad the smoke is this year, the grids will be more efficient when clean.
They said they expect containment by October 31 so we may have this mess for a while.