Ive just been setting a pi4 up with Ropieee.
Had the same issue as the OP for the first three attempts - just a 4 flash repeat and no activity showing on the LAN port. Was starting to think I had a dodgy pi as had re-flashed the card 3 times.
Anyway, turns out it must have been a bad card (was a new card also).
Cracked open a different new card - formatted, flashed and Bingo!
Must say, Im amazed at how fast from inserting the power cable to having Ropieee ready for login was - super speedy.
Have a zen DAC plugged in / powerd via the USB at the moment and it sounds great pushing a pair of A2C.