Increase transmitting range of doorbell

I’m also having significant issues with my doorbell camera connection both signal strength and upload speed. I have AT&T isp with a AT&T provided router of questionable quality. The router is about 40 ft away without any major wall or equipment obstructions. My doorbell camera is mounted on wooden studs which frame the door & entryway. The door is metal but the side panels are wood & glass near the doorbell camera. I’ve used a WiFi extender to try and improve the connection and it helps a little but the connection varies almost each time I recheck it using my SimpliSafe app connection checking (-55 to -65 dBm & 1.5 to 4 Mbs). I have moved the Extender all around the entry hallway both closer to the doorbell camera and closer to the router (1/2 way), with very limited improvement and still not consistently better connection.  I the bought the SimpliSafe recommended TP-Link extender and setup a new xxxxxx _EXT network. By adjusting its location I was able to establish a fairly consistent “good” connection to the doorbell camera. However, after a few weeks or a month the TO-Link & network attached camera would disconnect. This was more of a nuisance if I was at home (not on a trip), since I found unplugging the TP_Link extender would cause it & the doorbell camera to reestablish a connection. But there was no way I could do that when gone on a long vacation- leaving my doorbell camera useless for weeks/months until I got home. So I’m looking for a way to improve the connection still, including trying to improve the crappy doorbell antenna, changing ISPs, buying a Mesh WiFi setup etc.