Install Tailscale on your Pi and on any other device you want to access it from. It’s super straightforward and you should be able to connect the two devices without opening any ports instantly.

Benefits have been listed out here by others. The few restrictions I found on the free tier of Cloudflare is that they limit file size for uploads to 200MB. If you were exposing your NAS and want to upload a large file then you need to pay for Cloudflare or it will be restricted.