Welcome, @CDeWi.1, to the community!
Normally it is not necessary and would also be quite time-consuming/expensive to fill the vias with solder. If the filling is not carried out to a very high and monitored quality, you could face thermal cracking of the vias.
Maybe it would make sense to do a thermal simulation with all thermal parameters?
You could also use thicker copper plating to increase thermal conductivity?
Regards
/Peter
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