Question Cannot Maximize Video From Smart Phone To TV

[Casey2016]

I have an LG ThinQ 8 smartphone and a TCL Roku TV.
When trying to mirror from the phone to the TV, I can't maximize what is being transmitted from the phone to the TV.
Sometimes it works, others it does not and I don't know what I might be doing wrong.
Can someone help me figure this out?
Some videos will be full screen and others will not.....even though they did at one time.
I would appreciate any input on this as it is very frustrating.





I am able to view some You Tube videos and make them full screen but not all.

 

[Alabalcho]

How did you "mirror" the phone to the TV?

 

[Casey2016]

How did you "mirror" the phone to the TV?

I used the app called , "screen mirroring" on the cell phone.
Was able to connect through WiFi and whatever was on the phone appeared on the TV screen only it did not cover the entire screen.
Previously, I was able to enlarge the picture or video on my phone to full screen and then to the TV.
I have no idea what went wrong....if I clicked on something by accident or if it is a software problem.
Thank you for responding.
Casey2016