hi, with the laptop it is easier to exploit, but in the case of phones it is not so easy: the pin/lock is asked when someone tries to add a second device or create a backup so they can't just snap your profile there
besides that, to completely block access to certain apps, not only ArcaneChat/DeltaChat, android has a feature called "Private space" where you can protect with your lock/pin apps from being opened or even visible at all
in case it was in a laptop where it is much easier to steal since even if you could show an unavoidable warning about the profile transfer as discussed at https://support.delta.chat/t/dont-allow-to-delete-device-messages-chat-and-some-of-its-messages/4693 also the program data folder could be just copied, this is a problem of the low security of desktop systems, better never let anyone use your laptop in the same session as your personal session, you could have a guess session/user for such situations
if the worse happened and you suspect someone took your profile (which you would notice because some messages you didn't read are not notified and appear as already read), there is no safe way out of it, since your identity lives in your pockets in your devices (the encryption identity) and not in a server, if someone gets it the only safe way out is to create a new profile and tell everyone to block the older contact and remove the old contact from all groups etc
