How to save for something big like a house/appartement or car when your not sure if can spend the bitcoin directly?

Buy the bitcoin on a kyc exchange like kraken every month for multiple years(4 or more) so volatile markets are good.

Store the bitcoin coldstorage on seedsigner or trezor safe 3 or coldcard

If your not sure of the knowledge that is needed use https://keys.casa/

When you have bitcoin enough for the purchase and seller of the house don´t accept it directly. Send the bitcoin too a bitcoin exchange like www.kraken.com and sell the bitcoin for euro's and send it too your bank.

#SaveInBitcoin for the long term

#HaveNoFear

#SaveInEuro is stupid for a time frame of 4 years or longers