I understood that for FLASH of STM32L05x 1 bit error detection and correction is provided. What happens when more bits are corrupted?

[waclawek.jan]

I guess that lack of any further information means, that the FLASH module outputs the uncorrected (or incorrectly corrected) to the bus.

For more advanced ECC on FLASH with some signaling/interrupt, see the 'L4 subfamily.

I am not ST.

JW

[Tesla DeLorean]

Other parts generate an NMI

More generally you should checksum/crc memory to insure integrity and fail safely when you observe the array is corrupt.

You should discuss these issues with the FAE supporting your account. Pretty sure these devices aren't for systems where failure, or use in general, could result in death.