Shares held in crest are held electronically.
That's the only way Degiro accept shares.
I transferred CRH and BMW into Degiro, no problem.
I closed an account with Saxo and tried transferring all my shares to IBKR.
IBKR accepted all my shares except for CRH and BMW.
Degiro accepted these and were faster than IBKR.
You just need to fill in the downloadable Degiro share transfer form and email it back to them. They then contact your broker and arrange the transfer.