TPM has gone missing on a Dell 13 Inspiron 5379

I maintain my elderly mother's laptop. She has an Inspiron 13 5379. In the past, the laptop showed it had a TPM. I know the TPM was present and working because I enabled BitLocker for her (using the TPM). Recently I was helping her on her laptop and noticed BitLocker was suspended. I went to reenable it, but it wouldn't reenable. After some digging, I found that the TPM has gone missing. It is not showing in device manager and tpm.msc is saying there is no TPM. In device manager if I tell it to show hidden devices, then it shows the TPM. This is usually an indication that the device existed on the device in the past but has since been disconnected. Obviously the TPM hasn't been disconnected since it is soldered on the motherboard. I checked the BIOS/firmware of the device and there was no TPM option in the BIOS, so I can't reenable it. I also reset the BIOS settings back to factory default but that didn't help.

I did some searches in these forums and found a couple of other posts about the same issue with this model laptop. There was one suggestion to disconnect both the battery and CMOS battery and hold down power button for 30 seconds to completely reset the motherboard. I went ahead and did that and can confirm that the motherboard did reset because the date/time had been reset and I had to set the date and time. However, even after doing that, the problem persists. No TPM to be found. I also checked and her laptop has the latest BIOS update on it.

My only guess is that a BIOS update on the laptop for some reason erroneously removed the TPM as an option on this device, even though I know the device previously had a TPM. My question is - can this please be fixed via a BIOS update from Dell, or does anyone know what the last BIOS version was where the TPM was still present so I can revert back to that BIOS version? I did find the section for this device that has the older BIOS updates.