Changing the time signature

This piece is mostly in 3/4 but I wanted to have bar 176 in 4/4. But when I changed it, Dorico refuses to add the extra beat. See attached

In Dorico, changing a time signature does not add extra beats unless you explicitly tell it to.
This is important to understand.

In this case, delete the 4/4. Turn Insert mode on (I). Then enter the 4/4.
(Remember to turn insert mode off!)

(Edit: There are many threads you can read to explore the intricacies of time signatures in different situations)

Or select one of the quarter note / crotchet rests in the 4/4 and press SHIFT-B1q. This adds 1 quarter note duration.

Thanks!