High memory usage in Masters with MariaDB and Vitess
max_connections which is set to 15758.

Far too high.  Try 200.
Do those interesting mem spikes correspond to big queries?  Or garbage collection in Vitess?  &quot;Every week&quot; sounds like a backup by the host?
Do increase the buffer_pool to 2G, but not until you get the memory under control.
That the heck are those 12 things in the first image?