It seems this is a bug and hasn't been fixed yet.
As a workaround, you could have a button for testing and hide it when needed. Add something like this:
// JS query: previewFixed
(function () {
// 1) Start from your org + app info
const orgBase = "https://yoursubdomain.retool.com";
const appId = "yourUUID";
const appName = "Testing";
const page = "Link%20actions/page1"; // url-encoded path segment(s)
// 2) Build the correct URL
const u = new URL(`${orgBase}/apps/${appId}/${appName}/${page}`);
// 3) Add your own params first
u.searchParams.set("myvar", "test");
// 4) Then add Retool's release flag safely
u.searchParams.set("_releaseVersion", "latest");
utils.openUrl(u.toString(), { inNewTab: true });
})();