Ubuntu lacks the two characters U+2103 DEGREE CELSIUS and U+2109 DEGREE FAHRENHEIT.
Bugs #1319543 and #736613 are about Ubuntu mono lacking these characters, but the non-mono font lacks them too.
This is not often obvious, as on Ubuntu a fallback font is used. However it's not ideal since the C/F is obviously not in the Ubuntu typeface and the degrees symbol not the same size as in the Ubuntu font.
Presumably in order to be compatible with mono fonts where the degree symbol would otherwise take up too much space, some apps are using these characters instead of the separate degrees and F/C characters. For example, gnome-weather, the weather-in-clock gnome-shell extension, and the weather in the dropdown calendar in gnome-shell all use it (see attached screenshot). When I first set up my computer I had box characters instead in these places, because I only had set up Ubuntu fonts and did not have any fallback fonts with these characters. Now that I've installed more fonts it is better, but obviously not ideal.
I imagine it ought to be easier to fix this issue in the regular font than in the monospaced font, since fixed-width is not a requirement and so one can presumably just have it render the same as if the degrees and C/F characters were typed separately.
Note those characters are not the preferred encoding for these temperature symbols. GNOME Recipes used to use them as well, and I asked its developer to remove them: https:/