To do this what I did was added a column called IsCurrent. This menas that the user has 100s of login sessions but only one of them is "Yes" in the IsCurrent field. I use a lookup or filter to then grab that login from the SP List.
Filter(TimeLedgerV3, IsCurrent = "Yes") -> will give all the currently loggin in sessions in the list.
LookUp(TimeLedgerV3, IsCurrent = "Yes" And Name = User().FullName) -> this will return a users currently logged in session if there is one.
Is this kind of what you want to do or not? Here are my columns in the SP List although many of them are specific to the field this app was built for. (Auctioneering)

User's Name Start/End Times Hours Worked If current or not