Hi,
I have the same HW as you and update the FW regularly with the latest DiSlord versions. His project is very active and brings a lot of improvements:
It supports NanoVNA-H (default) as well as -H4 (config option). You can easily switch back to your 20211230 version if you're not happy.
There's no risk of bricking your device, just open it, connect the two pins of P1 and switch on -> DFU mode where you can load a new FW.
Or add one wire to enter DFU mode when you hold the jog switch down during power on:
/g/nanovna-users/message/10026If you want to see the 3.4 schematics just go to Hugen's place, he has also the newer HW revisions with SD card, that is supported by DiSlord's FW.
HTH Martin