Just download Squeak5.3rc3-19428-64bit.image and when try to update have
this.

This virtual machine is too old to support correct versions of the
FloatArray>>at:[put:] primitives 238 and 239.  FloatArray subclasses will
not behave correctly and FloatArray[64]Test tests will fail.  Please upgrade
your VM.  You may continue and upgrade later or abort and upgrade now.

Like know where is the correct VM.
In 
https://github.com/OpenSmalltalk/opensmalltalk-vm/releases/tag/202003021730

Exist many, so which is for macOS BigSur ?

Many thanks in advance

Edgar (bike keeper of Ferrari F1 team)
@morplenauta