That depends. I have a lot of things stored on the ICloud, so 128GB is enough for me.

It depends on your personal usage habits. For many people, 128 GB is enough to store a considerable number of photos, videos, apps and other files. However, if you take large amounts of high-resolution photos and videos or install many large apps and games, you could run out of storage space.

Using iCloud or a NAS (Network Attached Storage) can be helpful to provide additional storage space and a backup solution.

How I do it with 128GB

I still have more than enough free space and have the following on my iPhone:
Music: 105, Videos: 171, Photos: 4969, Apps: 79, Capacity: 128GB, Available: 87.24 GB

I use the iCloud and can easily manage with 128 GB. I have my music stored on the device (15 GB) and the storage capacity of my photos (approx. 65,000) is managed by the iPhone. I currently still have around 40 GB of free storage.