Of course, cloud storage is practical and – with reputable providers – also offers a high technical security standard.
However, access is naturally always via the Internet. If there are technical problems, if the provider ceases its service or goes bankrupt, or even if your Internet connection is down – you run the risk of not being able to access your data at all.
Also remember that non-European providers are not subject to European or even German data protection laws.
The regulations are sometimes very different from ours.
If the cloud storage is integrated into your computer as a network drive, your data can also fall victim to Ransom goods there.
So you can’t avoid a backup or at least backup copies on a separate storage. The GITZ offers a backup and archive service for organizational units of the TU Braunschweig (service catalog item 3103).
The German Federal Office for Information Security (Bundesamt für Sicherheit in der Informationstechnik, BSI) provides detailed tips on this at various points: https://www.bsi-fuer-buerger.de/BSIFB/DE/Empfehlungen/Datensicherung/datensicherung_node.html and https://www.bsi-fuer-buerger.de/BSIFB/DE/DigitaleGesellschaft/CloudComputing/GefahrenRisiken/gefahrenrisiken_node.html
See also: https://www.bsi-fuer-buerger.de/BSIFB/DE/Risiken/Sicherheitsirrtuemer/Sicherheitsirrtuemer.html?nn=7904670#doc7814992bodyText3