A friend of mine is using NextCloud, mainly for the file synchronisation. On her personal computer, she installed the windows client. On her professional one, she can’t install anything, so she uses her browser to “synchronize” manually her files.
For Owncloud I found (but have not tested yet) the two following clients :
This works. The settings are stored in \Users\username\AppData\Local\Nextcloud.
If you don’t want to store something on the computer, you can use the portable owncloud client on an external device. This works, too.
You can also download the client and open it as archive with e.g. 7ZIP Portable and unzip it to you Program folder except files and folder beginning with a “$” dollar.