Bulk insert Image blocks from URLs

You can use this plugin https://ww.wp.xz.cn/plugins/add-from-server/ which is written by one of the systems guys for ww.wp.xz.cn.
You probably would want something like https://ww.wp.xz.cn/plugins/format-media-titles/ active before you add the images, or maybe use https://ww.wp.xz.cn/plugins/auto-image-attributes-from-filename-with-bulk-updater/

By loading your images into the database this way, now they are accessible to any posts or pages that you write.

The original WordPress gallery is a shortcode (looks like [gallery]) which shows all images that are attached to a post. That means you can use it like that without having to go through the interface to choose the photos. But you would have to attach the images to the post somehow. You can do attaching in bulk also, using a plugin like https://ww.wp.xz.cn/plugins/upgrade-for-unattach-re-attach-media-attachments/
while in the Media Library using list mode instead of grid mode. Put a checkmark on the images to attach, then select the Bulk action.

I’m thinking you don’t want all 2000 images on one post, so you can organize your images using Media Categories, using a plugin to add that.
I don’t see any good way to add image blocks into posts except manually. I think the gallery shortcode is probably better. If you already have HMTL referring to your images (and that’s why you don’t want them to move), you can just paste that into a Custom HTML block or use the Classic editor and paste it in there.