With Accessibility enabled, there is a line of text displayed above HTML fields on the service portal
With Accessibility enabled on an instance, the HTML fields on the portal show a line of text that explains users on how to use the keyboard to use the controls for the HTML editor toolbar.
On the platform, this has always been shown as a help icon which can be clicked on to see the help text.
On the service portal, this text did not show up until Kingston but starting with London when the associated PRB for this was fixed, users who have accessibility turned on will now see a line of text just above the HTML field's toolbar.
This is an intentional change and this text will always show if Accessibility is turned on. There is no OOB way to hide this text with Accessibility turned on.