I've actually had the problem of hiding my accounts myself and have actually found a pretty good solution imo. I'm not going to fully into detail about it though, since it's a lot of steps you have to follow:
The idea of a show off account is quite good, as long as it's kept fairly active, your dad won't suspect anything. If you don't want to bother not having your previous searches and log-ins as in Brave, you can use a program called "portable apps" (https://portableapps.com/) and install your prefered browser using this software. Then you can even lock it with a password by using an Veracrypt (https://www.veracrypt.fr/code/VeraCrypt/) volume to encrypt the portable apps folder and only be able to access it with a password. In this volume you can also put other secret files, I for example have a diary for all my thoughts in there. The last step you can do, is to hide the veracrypt volume as SwiftySpeed showed.
If you want to open your browser with all your secret accounts (keep them seperate from your main showoff browser obv), you just find the veracrypt volume, type in your password and open the browser from portable apps. One thing you can to if your dad might just burst into room unannounced, you can use the multiple desktops feature on your pc and just switch to an innocent desktop by using Ctrl + Win + Arrow keys L/R, that way you can switch really fast.
If you want a good way to do it on your phone, the only really comfortable option i've found (I'm using a Redmi phone with MIUI, so Android), is to use the second space feature, where you can have a completely seperate phone from your main phone, which you can either access through settings, or you can even set a specific fingerprint only for the second space.
I hope these ideas can help you in hiding your accounts! The solution is a bit overengineered, but when I thought of these steps, I just wanted to be extra sure no one finds this account for example.