Hi,
Microsoft hasn't made any announcements of dropping support of RD Gateway (RDG). For your use case of just using RDG it is as you say--it is a tunneled RDP session, and they don't put a constraint on what passes through the tunnel, provided you have necessary RDS CALs for each user/device.
Windows Server 2022 End of Life is currently October 14, 2031, so even if it were the last version that included RD Gateway (they haven't said it is) you should be okay for several more years:
https://learn.microsoft.com/en-us/lifecycle/products/windows-server-2022
If the above was helpful please click Accept Answer.
Thanks.
-TP