The "Create New Review" page for Steam Curator groups is currently broken, but you can still post Curator Reviews using your web browser's console.

To post a curator review, do the follow in a web browser:
 1. Navigate to your Steam Curator group's "Create New Review" page.
 2. Open your web browser's "Developer Tools" panel. (Typically, this can be done by pressing the F12 key.)
 3. In the now-open Developer Tools' menubar, click on "Console" tab. (Located between the "Elements" and "Sources" tab).
 4. !! Read and understand this BEFORE you go to step 5 !!

You will be typing text (a "command" or "code") into your web browser's Console which creates a blank "Informal" curator review for a specified AppID—a Steam release (game/demo, etc.)'s "identification code". Note: the curator review created will also have the "I received this product for free" and "I received compensation to write this review" indicators checked. You can change that in step 7.

To find a Steam release's AppID, navigate to the Steam releases' store page and find the string of numbers near the end of the page's URL:
The command to *almost* use is:
(All " that appear are double quotes (a.k.a. quotation marks)—not single quotes).

However, you must replace the 🔴 with your target Steam releases' AppID. (Do NOT remove the quotation marks surrounding the 🔴; only remove the 🔴 itself).
Here are some examples of what the command looks like for certain Steam releases:
(Only type the command up to (and including) the semi-colon (;). Do not type any code after the semi-colon).

IMPORTANT: by default, your web browser prevents you from running pasted code in the Console. This is to prevent you from pasting/running malicious code. You can disable that protection, or you could just type the command in yourself. (I would advise you never run any code from an untrusted source).

 5. Type the command you came up with in step 4 into your Console and press enter.
 6. Go to your Steam Curator group's "Manage Reviews" page. You should see your newly-created blank "Informal" curator review listed.
 7. Edit the Curator Review you posted in step 5. Note: the command you entered will 'tick' the "I received this product for free" and the "I received compensation to write this review" check boxes. You may wish to untick those boxes if they are inaccurate.

To close your web browser's Developer Tools panel press the same key used to open it up (typically F12), or click the little 'X' in its top-right corner.

Also, I *think* Steam Curators groups can have a maximum of 2000 uploaded reviews at a time, so if you have 2000 reviews this probably will not work.