Devices constantly drop off the provided AT&T WIFI router - please help

I'll try to be brief.  New construction home with no options for internet except AT&T (former very happy Spectrum customer).  Paying for 1gigabit internet access, no phone or TV.  AT&T installed a BGW210-700 router. First couple of months were no issue.  Now almost all of my wireless devices constantly drop from the WiFi at least one daily.  From this forum and speaking to several AT&T employees, they all think it is the equipment.  I never have an issue with the wired connections from this router.  My question is how do I get the router set so that it is not the primary WiFi in the house.  I have a very nice NetGear WiFi router that I would prefer to use as my only WiFi.  I really dislike having to go through AT&T to manage my router.  I would much prefer if I could go from the fiber modem in my garage directly to my NetGear box.

Is this possible? and who would I go about getting this all setup?

2-story house.  Current router in closet of upstairs.  No cables run through the house, so relocating is not an option right now (Home was complete before we bought it).  Wireless devices throughout house (approximately 15 to 20).

Any advice would be greatly appreciated.

Thanks,