Same issue here on 2 different PCs with Opera GX not showing inventory informations
When logging into Amazon Seller Central, no products are shown in the „Manage Stock“ neither FBA nor FBM. As there would not be products listed.
Tried to turn off tracker and ad block without any change.
Using google Chrome is working fine and showing everything correctly.
No other filter or ad blocker is installed, so it seems to be only browser related.