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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 ...

For any case, see the ScaleRichView demos in Demos\Delphi\CustomDraw\Rectangles\
This folder has demos that draw rectangles:
- around all items
- around the item below the mouse pointer
- around the item containing the caret

I confirm the problem.
It will be fixed in the next update.
As a workaround, call ALabel.UpdateMe immediately after changing ALabel.Text.

I confirm the problem.
This is a drawing issue: the text is stored as not bold, but displayed as bold.

And I'm afraid I don't know how to fix this.

As I understand it, this is a result of font auto-substitution. The document uses the font 'Aptos', which is not available to non-Microsoft ...

In order to help, I need to know how you change content size in code.
Please send me a code fragment or (better) a simple project reproducing the problem.

See this topic for functions for calculating word count: https://www.trichview.com/forums/viewtopic.php?t=13

As for plain text, there are several methods.
For this task, the best function is RVGetTextRange(rv, 0, RVGetTextLength(rv)) from RVLinear unit, see https://www.trichview.com/help/idh ...