Hey ,
Lockdown mode will only work if you have vCenter Server but as I understand you are not providing that access to the user so in case you want the user to be able to access the ESXi by another user, you can change the root priviliege to No-Access or Read-Only.
Before doing this you will need to create a new user locally on your ESXi and provide administrator privilieges. For that follow the next document: https://blogs.virtualmaestro.in/2016/02/12/how-to-add-local-account-in-esxi-shell/#:~:text=Add%20users%20using%20ESXi%20host,User%20as%20in%20image%20below.
This will restrict the access completely to the host and the root user will have no access, however this will not impact the use of root inside SSH but I presume you are not publishing that to the Internet.
However, this is a solution to your issue, not a recommendation.