I’m happy for all of you who has successfully revived your reTerminal. I reflashed the STM32 according to instructions elsewhere, then performed the steps described by @tasman. Still blackness on both screen and HDMI. ssh still works, so I guess I will continue the struggle…
I think dmesg is trying to tell me something:
[ 6.642370] mipi_dsi 1-0045: I2C read id failed: -5