I have the same issue. I am running Bedrock on Windows 11 24H2 that has 64 GB of RAM. Memory consumption reaches over 95% within 5 minutes of joining my realm. There is a serious memory leak. The movement quickly becomes jerky and the game lags heavily in response to the controller. This version is completely unusable.
The memory leak exists even before joining a world or realm. I launch Minecraft Bedrock 1.21.120 and memory consumption continuously grows. It grows at a slower rate if I don’t join a world or realm, but it will still eventually max out memory on my Windows 11 computer.