How can I prevent unauthorized access to my Apple accounts from a Mac Sonoma in GB?

Why does GB Keep Showing Up on my accounts... Preferred User Language: en-GB Country Code: GB Keyboards: en_US QWERTY, emoji Emoji OS Cryptex File Extents: 786 Heaviest stack for the target process: 64 ??? (libsystem_pthread.dylib

Ive Asked Apple and they say nothing suspicious after im told there is something very suspicious going on by apple and they ask me if i have a mac sonoma which also keeps poppin up then im told agsin nothing suspicious... I Feel someone in GB witha mac sonoma keeps accessing my accounts thru the icloud via either contacts or mail with a passkey that kept asking me about with mac sonoma...my share across devices comes on one to two times a day.... I think they are using the business / work/ school account that i cant access and i fedl lime everthing im doing is being routed thru a pc which some apps i use are saying im using and using the app frim ... Can anyone help... Ive reset my phone woed factory clean at least ten times changing passwords do no good bc it always seems to start back up....

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