If your video looks good when in controlled conditions (no other WIFI signals around, close to the drone, etc) then its just a matter of getting the data to the phone in a more reliable way.
Dropped frames are mostly due to data that was lost on the way.
Solution is easy: Get a range extender.
The Xiaomi nano Youth router is the gold standard in the Bebop community, up to 4km range have been reported. Much better then the newer Xiaomi extenders, but hard to find these days. Personally I have done about 3,5km in perfect conditions when following a sailboat out to sea. Of course little Tello lacks the transmit power, sensitivity and MIMO capabilities of the Bebop so don't expect anything near this from the Tello.
Ideally put the router with a power bank on a stand / chair / rock a few meters away from you. My little Tello does 100m with (almost) perfect video using this router, 250m is fully reliable for FPV with some dropped frames, up to 400m is possible but risky. Just turning around can be enough to loose wifi signal.
But using a reange extender also opens up new flight regions, like going all around the house or behind trees in a distance.
If you want perfect video, consider wired ethernet between phone and router so there is just the WIFI connection between router and drone. Requires a cheap USB => Ethernet adapter. And of course a compatible phone with OTG support and ethernet drivers
But looking at the video quality of Tello I think this is too much effort given the results. Photos are impressive but videos are just barely OK.
