@AndrewL733 thank you so much for the reply and for all of the info!
I'll look into the Beelink systems, but I'm doing a user-to-router VPN with a few users that just connect to the OpenVPN in the Asus Router. There were no problems when we were using the RT-AC86U, but we just upgraded to the AX version, and I only have 1 user that is not working on the new router. I also just saw that you were also using the same router I was, the PRO version of the AX. I'm wondering if the non-PRO version might not have the same issue. I might try to find one of them and return the PRO router if that fixes the issue. Or I might just setup a software-based VPN on one of the systems to get the one user working remotely again, and hopefully if they replace their laptop soon we won't have the same issue for them or anyone else in the future.
I don't have much (barely any) experience with Linux, but one of my former co-workers was telling me about the approach you're using with PCs handling the site-to-site VPN. I'll talk to him about it some more though. Can you use just one linux PC on the internal network side and have external clients connect to it with OpenVPN or other VPN client software? Would that allow external clients to access all resources (network shares, RDP Servers, printers) just like they were inside the office? I was only able to get that to work with the Asus OpenVPN Server by using TAP, it would not work when using TUN.
I'll look into the Beelink systems, but I'm doing a user-to-router VPN with a few users that just connect to the OpenVPN in the Asus Router. There were no problems when we were using the RT-AC86U, but we just upgraded to the AX version, and I only have 1 user that is not working on the new router. I also just saw that you were also using the same router I was, the PRO version of the AX. I'm wondering if the non-PRO version might not have the same issue. I might try to find one of them and return the PRO router if that fixes the issue. Or I might just setup a software-based VPN on one of the systems to get the one user working remotely again, and hopefully if they replace their laptop soon we won't have the same issue for them or anyone else in the future.
I don't have much (barely any) experience with Linux, but one of my former co-workers was telling me about the approach you're using with PCs handling the site-to-site VPN. I'll talk to him about it some more though. Can you use just one linux PC on the internal network side and have external clients connect to it with OpenVPN or other VPN client software? Would that allow external clients to access all resources (network shares, RDP Servers, printers) just like they were inside the office? I was only able to get that to work with the Asus OpenVPN Server by using TAP, it would not work when using TUN.