Dear Osama Sabir,
First, my pleasure to assist you.
As per your description, please don’t worry, we can work together to narrow down and resolve the situation.
If my understanding is right, for the situation you encountered, we do understand the inconvenience caused and apologize for it.
According to this article IFS function and TEXTJOIN function this function are available in Office 2019. Here is my test result screenshot for your reference:
First, please updated Office to the latest version and check if you get these functions, or you may also re-install Office 365 and install the latest updates.
Also, I request you sign out from your Excel app> Close your all Office apps> Open your Excel> Sign in with your account> Check whether "TEXTJOIN" and "IFS" appears.
Also, I search a lot to find an issue cause, here I found one similar thread New functions for Excel 2019 are not available and they mentioned after e-installing Windows operating system, issue goes away.
In the meantime, I can’t reproduce the issue and to confirm whether this is a bug in a specific version, please provide us the version information. To check version: Open Excel>File>Account>Product Information and capture a full screenshot and share here (Please mask your private information) and we will be tested on that version and verify the result with you.
Your understanding and patience will be highly appreciated. I hope that you are keeping safe and well!
Sincerely,
Waqas Muhammad