Why is my select all button missing?

My select button is missing from my main outlook email. I am confused as to why it's no longer there as it is available for use on my other emails. I do not wish to switch to the desktop app or switch emails. I am aware that CTRL A/Shft + Click are options but I would like to have the functionality of just clicking to select multiple without the need of the keyboard. I have looked through all the settings I can find and even made a new account (this one) to see if there are any settings that differ that could've caused it, Unfortunately I found nothing helpful. I welcome any and all suggestions, relogging has also proved ineffective as well as removing all options from my toolbar and resetting it.

This tick icon is the one in question that has vanished.