You can Select the polygons with: `$area<10000` and [Eliminate selected polygons][1]:

> Combines selected polygons of the input layer with certain adjacent
> polygons by erasing their common boundary. The adjacent polygon can be
> either the one with the largest or smallest area or the one sharing
> the largest common boundary with the polygon to be eliminated.

[![enter image description here][2]][2]


  [1]: https://docs.qgis.org/3.34/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#qgiseliminateselectedpolygons
  [2]: https://i.sstatic.net/6jVPZ.png