Mооnst@r
Auto-translated
Does the site open on a smartphone?
If possible, please record a video of your actions when the "Error establishing a secure connection" appears, and screenshots from the "Network" tab, which can be accessed by pressing CTRL+SHIFT+E in Firefox (it needs to be opened before the site loads, otherwise it will be empty, or open it and reload the page, which will be indicated in the tab itself).
In the screenshot you sent, the browser shows that a secure connection has been established, so the error contradicts itself.
I can't upload images here because of the damn VPN extension.