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Please send me a project (as simple as possible) reproducing this problem.

I mean, this is the formula used by ScaleRichView internally.

Does your footer has height greater than 1/3 of page height?

Why do you want to do it?
ScaleRichView displays bottom margin large enough to include footer, even if PageProperty.BottomMargin is small (but the limit of 1/3 page height).
I.e.,
visible_bottom_margin = max(
PageProperty.BottomMargin,
min(PageProperty.FooterY + footer_height, PageProperty ...

It's by design.
This combobox is empty when the selected font does not exist or unavailable.

The font 'Aptos' is usually not available for non-Microsoft applications (you can check, can you see it in the font combobox?), so the font size combobox does not show suggestions for it. But the combobox ...

1) Do you want to apply the default font to new documents?
Find "Normal" item in rvActionNew.StyleTemplates, and assign it properties:
TextStyle.FontName := 'Georgia';
ValidTextProperties := ValidTextProperties + [rvfiFontName];
You can do it at designtime, or at runtime before the first execution ...

This is by design,

Your text has font "Georgia" applied on top of properties defined by its styletemplate.

When you apply a styletemplate, the results depend on the selection. If the selection contains multiple paragraphs, the styletemplate is applied only to paragraph properties. Text properties ...

This code must work:

procedure TForm1.FormCreate(Sender: TObject);
var
i: integer;
begin
i := RVEFilervActionNew1.StyleTemplates.FindByName(RVHYPERLINKSTYLETEMPLATENAME);
RVEFilervActionNew1.StyleTemplates[i].ValidTextProperties := [rvfiUnderline,rvfiColor,rvfiJump,rvfiUnderlineColor ...

There is no special method to reset StyleTemplates.

If you want to remove them in code, do it in the way shown in the topic https://www.trichview.com/help/idh_trichviewedit_changestyletemplates.html

RVStyleTmp.Units := RichViewEdit1.Style.Units;
RVStyleTmp.StyleTemplates.AssignStyleTemplates ...

I made the following test:

In the ActionTest demo, I edited rvActionNew1.StyleTemplates at design time. For "Hyperlink" item, I changed:
Color = clWindowText
UnderlineColor = clAqua
ValidTextPropertiesEditor (this is how ValidTextProperties are called in the Object Inspector) = [rvfiUnderline ...

When style templates are used, ApplyStyleTemplate(-1) does the same work as MS Word: paragraphs are formatted using "Normal" styletemplate, hyperlinks are formatted using "Hyperlink" styletemplate, all other attributes are removed.

Without styletemplates, we need to answer to additional questions ...

If you use style templates (rve.UseStyleTemplates = True), the simplest solution to reset formatting is calling rve.ApplyStyleTemplate(-1).

Without style templates, you need to define the meaining of "resetting text style".
Do you want to assign:
- properties of rve.Style.TextStyles[0] to all non ...

This problem will be solved by modifying TRichViewEdit.ApplyStyleConversion (and all other Apply* methods).
TRichViewEdit.ApplyStyleConversion will do nothing (and do not call OnChange), if this operation does not modify document.

The problem is in ApplyStyleConversion, not in the combobox. It calls OnChange even if nothing was changed. This problem is noticeable in TRVFontComboBox because it applies itself when losing focus.

This change isn't as simple as it seems at first glance.
We need to add checks to ensure that the operation has changed anything in the document. This requires numerous small changes in many places in the code. This will be added in the next update.

AFAIK, virtual constructors do not work in the way you expect.
Yes, TRVGraphicItemInfo.CreateEx calls inherited Create(ARVData), i.e. constructor TRVRectItemInfo.Create(ARVData: TPersistent), which is virtual.
However, even if you override this constructor in your class, TRVGraphicItemInfo.CreateEx ...