I find it it’s sometimes easier to import the text and recreate the document by applying styles (and building new frames if needed). It can save heartache with complex documents.
Always save in native .odt format as there is incomplete overlap between docx and odt. Some features might not be able to be saved in a foreign format.
@ajlittoz
Well, I want to use text box not frame!
I know that text box is a text placeholder (hold text only), and frame works as sub-document (hold text and other objects)! but I want just use text box. to put some text in some places in the page!
whatever the reason to use text box! there is a problem with its inside text alignment!
can you try using a text box and set text inside it to align to center and show me the result?!
I used frame and set align text to left, right and center! and no problem. look at this picture:
also I have used Ms Office in the past and no problem with text alignment of text box.
some one suggested me to use free Office, and I installed it on my Kubuntu and the second picture show you the alignment to center is perfect. but I do not leave LibreOffice!
With me:
Version: 7.3.1.3 (x64) / LibreOffice Community
Build ID: a69ca51ded25f3eefd52d7bf9a5fad8c90b87951
CPU threads: 8; OS: Windows 10.0 Build 19044; UI render: Skia/Raster; VCL: win
Locale: de-DE (de_DE); UI: de-DE
Calc: CL
Explain your purpose. Textboxes are almost always the wrong tool.
A frame can be positioned anywhere on the page in a deterministic, reproducible and reliable way. And thanks to frame style the same properties (position, appearance and more) can be assigned to several frames just with a double-click!
@Hrbrgr
same settings with me, but my text not at center exactly!!!
Version: 7.3.1.3 / LibreOffice Community
Build ID: a69ca51ded25f3eefd52d7bf9a5fad8c90b87951
CPU threads: 2; OS: Linux 5.13; UI render: default; VCL: gtk3
Locale: en-US (en_US.UTF-8); UI: en-US
Flatpak
Calc: threaded
Why Text boxes are wrong tool! 
if Text box is not useful, why it is a tool Ms Office and LibreOffice and many other text editors?! 
my purpose is to add text in particular places in page! and to form group of text in specific order and positions. like math equations.
In that case you must have a frame. Here are three ways you could use:
The simplistic way Click in the text so the frame is not selected but the text can be edited. Simply drag the slider to the right to align with the start of the margin of the frame as shown below
Or, also simpliistically, to right click in the text and select Paragraph > Paragraph > Indents & Spacing and under Indent change the Before text field to 0 or a positive number. OK
Remove Direct Formatting. If the style has been overridden by direct formatting. Click in the text so the frame is not selected but the text can be edited. Press Ctrl+A and the contents of the frame will be selected. Press Ctrl+M to remove Direct Formatting. The text should appear completely in the frame, if not then you will have alter the paragraph style (see below)
Modify the Style so it doesn’t have a negative indent.
@Hrbrgr
Perfect … “O” at the center exactly!
and I made a copy of your text box and change the text to " math" and still at center!
so what is wrong in my LibreOffice!
or the problem in my OS!!! Linux Kubuntu
thank you @Hrbrgr for your help! 
I hope one of linux ubuntu users give me a solution, maybe I have to install some dependencies or Libraries to my OS! 
thank you for your answer and pictures!
you said a I must have a frame! but what is wrong with text box!
I do not have a problem with frame alignment, but it is not for text only! it is a container for text object and pictures … etc as a grouping method as sub-document.
it seems heavy on document when I will use it so much.
what I need is text box, it is not heavy, and I can use them to make a composition of text in specific shape and order. like math equations. frames can not group together.
@Alaa.Sami these are probably translation misunderstandings
@EarnestAl assumes that you are talking about a text field in your given example, but it is actually a frame.
So it is not about whether something is wrong or right.
Take another look at your document example to see if it really is a text field or a frame.
Or better upload the file here to be able to examine it.
With 7.2.5.2.0+, exactly centered
Text boxes in M$ Word and LO Writer are not the same. In Writer they are “foreign” graphical objects and they don’t coexist easily with text. If you insist on ease of use and “intuitiveness”, stay away from text boxes. You’ll have more trouble with them than with frames, notably to prevent overlap. Note that the configuration GUI is much worse than frames, forcing you to go through many dialogs instead of just one and with the impossibility to save all settings in a style.
Then compose the contents of your “boxes” with Math, the formula editor.
@ajlittoz , I don’t have the problem of needing to be convinced, but sometimes the right path is a long one.
It might be a bug in that case. I cannot force text outside a text box in Windows 11, LO 7.3.1.3 but there was something vaguely similar in tdf#12440 (fixed) so it could happen
First steps to take before submitting a bug - The Document Foundation Wiki
How to Report Bugs in LibreOffice - The Document Foundation Wiki
If first steps doesn’t resolve issue then please report bug number here. Use the format, tdf#12345 ,and the number will become a link.
I notice in your screen shots that the text box is using the Default Paragraph style. Have your checked you settings for this style? Particularly, check the settings under the Indents & Spacing and the Alignment tabs.
Paragraph styles cannot be applied to text boxes. As I mentioned above, text boxes are not textual elements but graphical objects handled through different principles than text. Strings in text boxes can only be direct-formatted.
Thanks. I learned something new.
