The best is to have a secret phone like secure folder or private space. Thus you are protected even if someone makes you unlock the phone.
Like a folder? Probably noticeable with a utility like WinDirStat.
Like a separate user? Can the other one install apps? If so, you're likely done for if someone gets access to the one account. Also there's this [1] to consider, as well.
I hate shooting privacy ideas down. Unfortunately, that's all I have to contribute this time.
After using it I like the idea with Huawei Private Space. You need to unlock the phone with a different biometric/password to get notifications even. So separate storage / user / app store.
Samsung Knox is a bit more seamless, you can choose how much you share (like copy & paste).
In case you are made to do it both can fool goverment to accept that you phone is clean with the correct setup.
Both have separated contacts / app store etc and are separated with support from the hardware.