Are you wanting to select a template that will be used to display the page, but the only option is “Blank”? The fact the rest are briefly visible indicates they were all output from the server, but something client side is removing or hiding them. I suspect your theme or one of your plugins is unintentionally behind this behavior.
To narrow down the cause, switch to one of the older default themes, 2021 or earlier. Also deactivate all plugins. Default themes likely do not have multiple page templates, but an alternative page template can be created for testing purposes. Make a copy of the theme’s page.php or index.php template, naming it something like alt-page.php. Right below the initial <?php tag, insert this line:
/* Template Name: Alternate Template */
Save the edit.
You should now have two page templates to choose from, Default and Alternate. Restore your plugins, one at a time, testing after each. If the template choices again disappear, the last activated plugin is the cause. If you are able to restore all plugins and still see the choices, the problem lies within your normal theme itself. Take up the issue through the dedicated support channel of the module responsible.
