what do you have configured in "Force HTTPS"?

please take a look at PR #8619, this PR (or a newer version of it still to be developed - I'm sorry it's not yet complete) will hopefully handle this accordingly:

• configuration of HTTP and HTTPS ports
• switching between HTTP and HTTPS according to "Force HTTPS" setting and "usesecure" setting

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  _{This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/11213.}

I am afraid it is nothing to do with Force HTTPS setting. Speaking of "Force HTTPS". I find 3.6.0 recognize only port 443 is valid HTTPS port. If my site other than 443, I could not event set "Force HTTPS" to other than "None". It gives me the misleading message:
Warning
HTTPS has not been enabled as it is not available on this server.
Message
Configuration successfully saved.
And the setting falls back to "None".

I had an older Joomla 3.4.5 running on high port number and its "Go to site home page" and "Preview" links simply follow my current URL and my Force HTTPS there was simply None. I really want that feature back.

There was a change in 3.6.0 when you try to set "Force HTTPS" from None to anything else. The check implemented shall prevent you from locking out of your Joomla installation if you cannot connect to your server using HTTPS. You're right that currently HTTPS is only supported via port 443 but even that shall be changed by means of #8619 (two new fields holding the HTTP and the HTTPS port numbers you use, if empty the defaults - ports 80 and 443 - will be used).

But I tink that even before 3.6.0 it was tricky to set "Force HTTPS" to e.g. "Administrator Only" if you're using non-standard ports. After saving this setting and opening the next backend page Joomla automatically tried (and tries) to switch to HTTPS protocol unless you manually opened the backend via HTTPS. And with any HTTPS port other than 443 that would fail.

There was a change in 3.6.0 that causes all links from the backend to the frontend (preview links) to be converted to HTTP if "Force HTTPS" is not set to "Entire Site". But if you set "Force HTTPS" to "Entire Site" your preview links from the backend to the frontend should again work, even if you use a non-standard port. Yes I know you currently cannot change this setting via the global configuration since the HTTPS check fails but you might modify the configuration.php file directly (this is not the desired solution but only a workaround until you can configure the HTTP and HTTPS ports to use).

@kenleegit does the answer above solve your issue with using non-standard ports etc.

Dear @jo-sf,
Thank you for your advice. I got it working. I can live with that.

Dear @brianteeman,
Thank you for your follow-up.

Closing