The iPhone 4 doesn't support 5G, but it would still work on the 4G LTE network and the 4G LTE network isn't going anywhere any time soon. The CDMA network is being retired so at some point you will need to replace the phone with a compatible VoLTE phone, but Verizon Wireless should notify you when you need to replace it by.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
The iPhone 4 is an older phone, but it was certainly not set to be inoperable because it doesn’t support 5G.
It may be time for a new phone if you can’t get it to restart again, but only because it has naturally reached the end of its life, not because it is not compatible with 5G.
I can understand how important it is to use this device. This device is a 3G Model Phone not a LTE/4G device. You can view detail on our CDMA Network Retirement here https://www.verizonwireless.com/support/knowledge-base-218813/. Did anything change on the device, when this issue started? Are you able to press and hold the Power and Home Button for 30 seconds to force a restart? - AlbertoR_VZW