Yes, currently if you want to do it in a large range you will need to do it thanks to PowerShell.
In this scenario, you can use the PowerShell module called AzureAD and use the following CmdLine to be able to add members to your Azure AD Group : https://learn.microsoft.com/fr-fr/azure/active-directory/users-groups-roles/groups-settings-v2-cmdlets. Azure AD module can be installed easily by typing the command : Install-Module AzureAD from any server that is able to reach Internet. Then, you can see all the available commands by doing the command : Get-Command -Module AzureAD and the CmdLet that will be useful for you will be : Add-AzureADGroupMember. Are you confortable with PowerShell ?