Can I upgrade the SSD in a 2014 MacBook Pro 13-inch with a standard NVMe drive?

No, the 2014 MacBook Pro 13-inch uses a proprietary PCIe 2.0 x4 blade SSD with a 12+16 pin connector, not a standard M.2 slot. You can’t just drop in any NVMe drive, but third-party adapters exist if you’re willing to tinker.