Timing Advance(TA). it's calculation capabilities with MONs

we all know that Timing Advance is used to control the uplink transmission timing of individual UE.
My question is: are the operator’s devices able to store the timing advance for all active and idle UE in a specific cell? For example, in some specific CELL of BTS, there may be 3000 subscribers that are feeding into that specific sector, and 50% of those customers are in Active and 50% are in Idel Mode. Is it now possible to recognize all the 3000 UEs by the VLR, or do the 3000 UEs introduce themselves to the VLR after each and every 5 minutes?
any solution?

Only active UEs will be UL synchronized and their timing advance information is maintained by BTS. For idle UEs there is no need for UL transmission, so no need to maintain TA.

Thanks, Mr. upf. Is it possible for MNOs to maintain information about idle UEs within a specific cell through the BTS? Please, can you tell me which tools or resources we need to upgrade for maintaining information on the idle UEs by the BTS?

BTS has no information about idle UEs. Only MSC/VLR, MME or AMF know the reachability of idle UEs.