Transfer Render $RNDR (+3,06 %)
from Bitvavo to Bitpanda is not offered by Bitpanda, but Render is available at Bitpanda - was also confirmed by Bitpanda support

As I want/need to hold for longer than a year because of the tax treatment, my question is: transferring to a cold wallet like ledger shouldn't be a problem, should it?

PS: Swap to Solana or similar is not possible. This is treated like a swap to a fiat currency.