Cannot DFU revive macbook air early 2020, any way to retrieve data

To attempt to retrieve the data, try booting into Target Disk Mode...do this now before trying anything else if this data is important. This is your only hope to recovering data if you cannot boot the laptop if you have no video on the display. Target Disk Mode now requires using a Thunderbolt USB-C cable (one with a lightning bolt on the connector).

You can try using an external display to see if you get any video on the external display just in case the built-in Display Assembly has a hardware issue.

Is this an Intel or M-series laptop?

What version of macOS is being used on that laptop?

Do you see video when accessing the Startup Options or Option Boot screen (M-series & Intel respectively)?

Can you boot into Recovery Mode?

If you cannot access the Startup Options screen, then perform another DFU firmware Revive. After it completes if you are asked to Authenticate, then do so, but then select "Shutdown" (first press the Caps Lock LED so it is lit...the laptop is completely powered off when the Caps Lock LED goes out). Then power on the laptop and boot into Recovery Mode.....do not let the laptop attempt to boot into macOS or you may need to repeat this again).

Once you boot into Recovery Mode, launch the Terminal app from the Utilities menu on the menubar and issue the following command to clear the NVRAM settings.....sometimes the NVRAM may be configured with a setting this is incompatible which can prevent normal booting...this command is safe for both Intel & M-series Macs (this has fixed some M-series Macs with boot issues for me):

nvram  -c

It is possible you may see permission denied messages regarding some settings especially related to computer names, but you should not see an error regarding the command itself. If successful, then try rebooting the laptop to see if it will boot. I would suggest booting directly & immediately into Safe Mode to maximize the chances of booting.

You can also try reinstalling macOS. Ideally it is safer to install macOS into a new APFS volume assuming you have at least 80GB+ of Free storage space on the internal SSD (check Disk Utility to confirm the amount of Free space....ignore the "Available" space value as it is very misleading). If you don't have enough Free space to install macOS beside itself, then you can try installing macOS over top of itself (I have had this work a few times on an M-series Mac). Or you can install macOS to an external USB3 SSD (If an Intel Mac, you will need to first modify security settings to allow booting from USB by using the Startup Security Utility).

Again, if you don't have video on the screen you may need to perform another DFU firmware Revive, then immediately after completion boot directly into Recovery Mode. If you accidentally miss accessing Recovery Mode & start to boot into macOS, then you may need to perform another DFU firmware Revive to restore video functionality).

If you have an Intel Mac, then you may find it easier to do an Option Boot, then press Command + Option + R while sitting at the Option Boot screen (aka Apple boot picker menu) to access Internet Recovery Mode to bypass local recovery mode which may be broken. If you have an M-series Mac, then you only have one option for accessing Recovery Mode (holding the power button until you see "Loading Startup Options".

Yes, these steps are annoying & may need to be repeated if you miss the window of opportunity after the DFU firmware Revive. Sometimes you have just one chance to do something after the "Revive" procedure, then the laptop is stuck again where the "Revive" is needed to unstick the system again. I have personally used these steps to get some of my organization's Macs working again. I have spent an entire day performing the steps outlined here multiple times because it is very easy to miss the moment of opportunity after the "Revive". I have come to despise these 2018+ Macs because of this and having no visual cues to what is occurring with the system in order to gather clues to the problem.

Otherwise the data is most likely not retrievable unless you contact a professional data recovery service to see if they can do anything, although that will likely be expensive. Some will provide a free estimate such as Drive Savers.

People should always have frequent and regular backups of their computer and all external media (including the cloud) which contains important & unique data. There are a lot more new ways to permanently lose access to the data on the internal SSD of the recent Macs due to all the hardware, software, and security changes. You just encountered one of those new ways of losing access to the data (the data may be perfectly fine on the internal SSD, but there is just no way to access it).

FYI, I seriously doubt a DFU firmware Restore will make any difference assuming you correctly implemented my suggestions above.

I don't recall how the Intel Macs behave after the DFU firmware "Revive" process has completed. If you hear a chime, then make sure to immediately hold down the Option key in order to access the Option Boot (aka Apple boot picker) menu. You should see something on the screen if successful even if no bootable volumes are shown. If you are on the Option Boot (Apple boot picker) screen, then just press Command + Option + R at the same time to have the laptop boot into Internet Recovery Mode.

If you are unable to access the Option Boot screen after the DFU firmware Revive, then I think you will need to have the laptop examined by Apple or an Apple Authorized Service Provider. Personally I would not spend any money on repairs since the Logic Boards on the 2018-2020 Intel MBAirs are not that good (very poor cooling system as well). The money spent on repairs would be better spent going towards a new laptop.

Apple Configurator can definitely help provide clues as to the state of the laptop when there are no other visible signs. I don't know if having the host Mac connected to the MBAir will cause any problems booting the system into Internet Recovery Mode.

Edit: Here is an Apple article with instructions for performing an SMC Reset (read the instructions carefully since the process has changed from the older model laptops):

Reset the SMC of your Mac - Apple Support

Here is an Apple article for a PRAM Reset as well (hold it for two chimes if possible, but some T2 Macs won't allow it to be held for a second chime).