Thunderbird 115 and above requires the ability to use the default title bar of the Linux desktop environment to avoid button redundancy in environments such as XFCE 4.18. Like my ever perfect Firefox-esr
Sorry. My idea is a terrible error. It's posible set visible the titlebar in new versions Mozilla Thunderbird. So, no problem with button redundancy in Linux Desktop Enviroments like Xfce. The setting is in a new plase, we must search it. ✌️