The button Launch HTML in not shown under the User Profile options in the responsive UI.
Cloud for Customer responsive UI
The Launch HTML button is deactivated if the user personalisation changes are deactivated in HTML under Company Settings. In pre-1802 systems, this is done by graying out the Launch HTML button, in 1802 system, the button is not shown.
Use following URL to open HTML and activate end user personalisations under Company Settings:
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SAP Cloud for Customer add-ins all versions ; SAP Cloud for Customer core applications all versions