Might be a bug here. See attachment.
when I try to make a slur between the first f and the g, the slur attaches to the second f instead.
Furthermore, the slur won’t delete or undo.
the order of entry was
4/4
first f 8th, (top voice)
new voice.
g whole note (bottom voice)
second f 8th, (top voice)
[ left picture ]
ctrl-select first f and g, slur
[ right picture ]
You can’t slur those two notes together, since they’re in different voices with adjacent rests present. If you want that slur, your whole note needs to be the same voice as the pickup eighth. Easily done—you can always add another upstem voice for the next eighth.
I believe you can select (highlight) the notes you want (F and G) and then input the slur (S). That should also work. I do this when I’m tying from one voice to another (but obviously I use ties instead of slurs in that case.) I believe the functionality is the same with slurs. In your case, it may require some work in Engrave Mode since the slur will be reluctant to bend down towards the G because of the rests.
As James says, you can certainly slur the G to the F, provided you select each note with Ctrl+click and then hit S. There’s also no restriction on deleting slurs, so it should be as simple as selecting it so that it is orange, and hitting Delete. If you find that not to be the case, please attach the project here (zip it up first) so we can take a look.
Easiest solution is to click to select that whole second bar, and “Swap voices.” Then the eighth and the whole note will be in the same voice, and the slur will notate correctly.