Perhaps you can first check a “Managed Nextcloud” in the internet.
You can test nextcloud without install anything.
You can upload non-confidential data.
I think “Managed Nextcloud” and internet is not slower than Pi4 and LAN
You can use an 60 minutes account.
You get an user name e.g. “XficAHBZrXmyF6mb”
The password is: demo
You get the server https://demo1.nextcloud.com or https://demo2.nextcloud.com
Because of a certificate error create an account at https://demo2.nextcloud.com and not at https://demo2.nextcloud.com . If you get “demo1” repeat creating test account.
Now you can install e.g. nextcloud clients and use the data:
After 60 minutes you must create a new user.
You also can get an free account: