When attempting to update vSAN witness appliances to match the same version as ESXi you may not be shown the most recent versions as available options using baselines or image based updates/upgrades.
VMware vSAN
VMware ESXi 7.x
VMware ESXi 8.x
VMware vCenter 7.x
VMware vCenter 8.x
The download repositories are now protected by a token based authentication and not able to sync the more recent versions of ESXi to be able to perform the update/upgrade.
Please refer to the following KB to make sure you have obtained and configured the necessary tokens/URLs:
VCF authenticated downloads configuration update instructions