The last OpenVPN server update was in March, but you say your Linux client still works. I am testing with Win11, OpenVPN (Community) 2.5.5 and using a laptop connection via my phone and it sucks. It took a while to connect. Having connected, it took the laptop a long time (5 min+) before it would route to my LAN. The shared folder listing was OK, but the subsequent download is stuck. I have no idea if this is a Windows issue or a Server issue or a poor data connection (but my phone gives me 3 bars on a 4G connection). This is pants.
Then my mother connects to my LAN by OpenVPN through her cable connection. Taking control of her PC with VNC and browsing a share on my LAN and downloading from my LAN was very fast so I don't know what to say. Her PC is old, Win10 with OpenVPN 2.4.8.
There are too many variables to know why my laptop > cell phone > me was slow. My mother's desktop to me was totally acceptable.