How fix fonts on external tv look good view?
It sounds like your TV is not correctly connected to the Mac, so that you only have Full HD resolution available instead of the UHD resolution you want.

I would suggest trying with a different cable from mini-DisplyPort directly to HDMI. This should give you the least amount of problems connecting to the TV. Ensure that the cable specifically supports 4k.

I have seen multiple times that even cables sold as HDMI 1.4 cables do not really support 4k with the Mac (I guess some companies deliberately re-label old cables). Specifically I have seen this also with expensive cables, where as a cheap HDMI cable from IKEA works without any problems.