I would like to change the font and size of text in text box - not PDF
To change font & size of text
1 Left click on your textbox text to make the textbox active
Note when you do this the Formatting toolbar will be switched off (I don’t know why - does anyone else here know?)
2 Double click inside the textbox to show the text cursor.
3 Select the text you want to change (Shift>Arrow Key or use mouse)
4 Select Format>Character to open a dialogue where you can choose the font, size etc.
As an alternative to step 4 select View>Toolbars>Formatting to turn the formatting toolbar back on and choose your font, size etc.
I hope this helps. I fear I don’t know what you mean by “not PDF”. If you alter the font in Writer then save as a PDF then the altered text will appear there. This is as I would expect.