From the point of view of cryptography, the block is sufficiently protected against such attacks. Quantum computers and quantum computing also do not pose a threat to hashing functions and the blockchain itself.
attacks by rebuilding the chain of blocks are real and depend on how well the shares of those participants who participate in the creation of blocks are distributed, where the shares can be measured both in computing power and other quantities depending on the consensus algorithm. The real danger is only short-term attacks on the last few blocks of the chain. To avoid risks, you must wait for a certain number of blocks to stabilize the chain. From practice for Bitcoin it is enough to wait for 3 blocks.