I am usually able to repair my furnace, however this problem is baffling me

In fact, this week was the first time that I ever called the Heating and A/C company to fix my furnace since I have been an adult

At my house, I am an Heating and A/C company, technically, I am not a certified Heating and A/C company, however I have been fixing Heating and A/C units for so long that my children would be surprised that I am not an Heating and A/C company, however i grew up in the kind of condo where my dad could fix anything; My dad was the electrician, mechanic, plumber, plus Heating and A/C company… Sure, my dad didn’t constantly fix the problem with the Heating and A/C units faster than an Heating and A/C company would have, although she knew enough to keep the furnace plus the central cooling system running, plus she passed all of this expertise onto me. My partner was so surprised when I fixed the furnace in our house for the first time after we got married. She couldn’t believe that I knew how to fix the furnace, but her dad constantly called an Heating and A/C company to fix the Heating and A/C units whenever they stopped laboring. I have continued to fix the Heating and A/C units since then, plus there have only been a few times where I came close to calling an Heating and A/C dealer, however I didn’t. In fact, this week was the first time that I ever called the Heating and A/C company to fix my furnace since I have been an adult. My furnace stopped laboring last week, plus I have tried everything that I can suppose of to fix my furnace, and at this point, I don’t want to spend any money replacing every section of the furnace. I decided to call an Heating and A/C company because it is my only option. I believe that it will be high-priced, however so will replacing my entire furnace if I can’t figure out this problem.

Air cleaner