Hi,
RDWeb server integrating with RD Gateway maybe a solution for your requirement.
You could publish your remote apps on the RDWeb server and users will connect to apps from a supported browser by a URL of the RDWeb server (https://rdweb.domain.com/RdWeb). Since you would not like to use VPN, you will need to first register the domain name for the web server and use the RD Gateway to guarantee the security.
Please refer to below blog for detailed steps of RDS deployment with RD Web Access and RD Gateway.
Deploying Remote Desktop Services 2016 Step-By-Step
https://nedimmehic.org/2017/01/21/deploying-remote-desktop-services-2016-step-by-step/
Hope the information could help.
Thanks,
Eleven