Your upload is choked. Fiber actually helps here.
Most cable plans ship asymmetric — a '1 gigabit' plan often has 35–50 Mbps upload. That's fine for browsing. It's not fine for Zoom + Dropbox sync + a security camera + a Twitch stream. Video calls drop because outbound packets are queued. DSL and 5G home have the same problem, worse.
Disable iCloud, Dropbox, OneDrive, and Google Drive sync during meetings. Turn off phone photo upload. If your calls stabilize, you've confirmed the diagnosis.
Some cable providers now offer mid-split DOCSIS 3.1 with 100–300 Mbps upload, but you'll need a compatible modem.
Symmetric upload is fiber's killer feature. A 500/500 fiber plan will feel faster than a 1000/35 cable plan for anyone on calls, uploading content, or running a home server.
ZIP for quick check, or full address for census-block precision.
Try any US ZIP — we query the live FCC dataset. Example: 29680, 78704, or 94110.