By default SQL Change Automation deploys changes within a transaction (and it uses the SERIALIZABLE transaction isolation level).
Full text objects can't be created inside transactions.
A SQL Change Automation build always start by deploying the project to an empty database (schema validation), so this issue is more likely to occur at this stage.
To workaround this issue you should use the NoTransactions SQL Compare option.
Please note that if you use this option there's no rollback if the deployment fails so it's advisable to isolate changes that require this change as much as possible and backup the targets before carrying out the change.
Setting the SQL Compare options in the Azure DevOps add-on: