Selcuk Keles

As @Randy Calvert already mentioned in his reply above, it's not possible. IPS offers only the download for the latest version available.
Unless you saved the ZIP file of the 4.6.3 files you won't be able to download it anymore.

You can’t. You need to upgrade both to the latest version. 

That is indeed the only native way to achieve this. In honesty, I would be trying to find somewhere to restore it where you can upgrade, just to do the conversion. 

You can convert content from another invision site to an existing one, but you would need to make sure they are both on the latest release first. You would then use the conversion tool. You can see more about how to use this here
 

Hi @Selcuk Keles,
If you are receiving the notifications every day after hiding it until tomorrow, then it is actually doing its job.
There is no way to remove them entirely as the intention is to inform our clients that PHP 7.4 is reaching end of life and no further security updates will occur on communities using older versions of PHP. It will only be a matter of time before you encounter issues. Just to put it into perspective, PHP 8 was released on 26 November 2020. We want to ensure our clients are up to date and don't expose their communities to security vulnerabilities in the long run.

IPB support fixed the issue :
MySql server "Server connection collation" was "utf8mb4_unicode_ci"
They changed my DB and table collations to "utf8mb4_unicode_ci"
All of characters are Turkish in tables now, and forum displays as is.
Thank you.
 

The behaviour with new posts is what it has to be. 
I am afraid ( and I hope I am wrong ) you will need to convert the old posts to look normal. That was what I had to do long ago when I was using SMF .. I hope support has a better solution for this..

The solution may not be that simple. with cong_global having sql_charset as utf8 can you do a test and post a message to board with Turkish characters and see how the records look like both in forum and db ? If all look ok  you may need to do something with db.

Hi Selçuk,
Normally when collation of DB is set to UTF-8 and configuration of the forum has the charset="utf-8" setting you should see all characters in Turkish form both in forum and DB. That is what I see in mine at the moment.