After 1/2 year of learning how to building the frequency scanner the work has paid of. I found out that it's not worth to use any RTL-SDR key, because the key is not compatible with the Raspberry Pi. The program was lagging or It wasn't able to find the RTL-SDR keys/USB port issue/. Therefore, do not waste your time with RTL-SDR and rather invest your money into more efficient hardware, such as RSP1A, RSPDX. You will find this hardware more stable and value for your time.
My current configuration is: Raspberry Pi4/8Mb Ram, RSPDX, HighEndFeed 30m long antenna for HF and for VHF/UHF Diamond X-500. This device outputs is under 24 Mhz reference clock frequency-locked to GPS signal. Scanner is available for max 3 users.
Good luck! Stefan - OM2ABC