Avoid splitting a note with a tie

AvoidTie
I have tried note grouping, Force Duration, but cannot persuade Dorico to show a crotchet rather than these tied quavers.

Welcome to the forum @Figaro47 !

Select the tied Cs, then press O, then 5, then 6.

This is to force the duration, then change it to a duration that can be notated using a single notehead, then bump it back up to a quarter note (crotchet) again, but with Force Duration now active, Dorico knows to show it as a single quarter note (crotchet).

Or, if this happens a lot: consider changing the time signature. For example, in cutc Dorico uses that spelling automatically (albeit with some amendments to the back half of the bar, which you might need to tweak some Library > Notation Options > Beam Grouping settings to fix).

Forced duration should work: Select the tied note, press O, then 5 and then 6.
Does this work?

Lillie is so fast!

Thanks Lillie, splendid!

It does, thanks!