The quarter-half-quarter pattern is a Dorico recognized syncopation. Unless other parts somehow change how Dorico interprets it, you may have to use Force Duration to split the half note at mid-measure.
Ah, that makes sense. Thank you!
Thats one setting that kept tripping me up, until someone pointed it out in another post
Actually, in this case you don’t want that setting checked.
I too am still struggling with Dorico changing my note values and/or adding ties. I am not inputting multiple voices - just one voice. I have tried Force Duration & also Pitch before Duration but without much success. Any basic advice, sorry I am still a beginner
Force duration will always put in exactly what you specify (assuming it’s numerically correct for the bar) but you have to have it activated as (before) you enter the note.
As mentioned further upfield of here, there are notation options for how Dorico inputs certain rhythms by default, in keeping with various customs of music theory. If you’re finding yourself fighting Dorico, odds are you have the wrong option ticked for your needs, or you’re likely trying to bend common practice. As long as it’s the latter and intentional, and not due to lack of musical understanding, then force duration is the way to go.
thank you , Romanos, for taking the time to give me your valuable tips. And I tried again Force Duration successfully.
Although I still had a problem putting in a whole note. Dorico would enter other notes despite having first selected Force duration. Then I also tried Pitch before duration unsuccessfully. The only way I could enter a whole note was by changing the rhythmic grid to a whole note. But this move seems rather odd
Odd indeed… 
Maybe you can provide a little more info about the piece and what you are trying to do? 
I agree with @YourMusic.Pro : something seems fishy here, and I suspect we can help you root out the cause with a little more info.
Can you tell us the exact sequence of events when entering a whole note did not work for you? Or perhaps upload a dorico file where the problem seems to manifest?
Just by way of example, I’ve made a nonesensical bar of 37/8, and even here, Dorico will respect a whole note as long as I press O before I enter it.
The first note I enter, Dorico tries to respect beat boundaries according to the notation options of the document, but the moment I press O, everything is as I instruct it to be:
I completely concur, my issue is slightly different from yours but it is still extremely annoying. Dorico keeps turning on dotted notes despite the fact that I have literally turned it off THREE TIMES. Frustration is one thing but when a piece of software is unintuitive sometimes you have to use capitals to highlight what you think is fundamental design flaws. I switched from Sibelius which was awful, to Dorico which also has many issues 4 or 5 years ago. As a hobbyist I constantly still battle with it. I understand part of my pain is caused by the fact that professional musicians need to have efficient tools. But I still believe the way Dorico is set up must actively infuriate others and work against them getting ideas down on paper. When I read your posts I did not read aggressive, it was merely direct. We don’t all think and work in the same way and that’s a good thing. And what’s unintuitive for me is completely sensible for someone else. Most of the time I have no idea how to turn off certain behaviours in the menus. I would prefer if certain things like Flow headings turned off and not on by default for more involved pieces. As for the complexity of expression maps if I forget to use one of my downloaded BBCSO templates I am simply scuppered and have to spend time copying everything across. Anyway that’s my issue not anyone else’s. Thank goodness for forums.