welcome in the forum.
First of all, never used Silva for Fungi but glad to learn it contains that too.
Can I ask you if you can provide the full command you used for that?
In general, any qiime2 plug ins works with qiime2 artefacts as input.
I suspect you trying to import the database sequence references and the respective taxonomy in qiime 2 artefacts, for this please have a look at the tutorial on how to prepare a reference https://docs.qiime2.org/2020.2/tutorials/feature-classifier/.
On preparing the reference, please be sure to that the taxonomy you using is all at 7 levels and with the format compatible with qiime2 (in general Silva taxonomy is usually compatible with qiime2 but it may contains many more taxonomical levels).
My final point would be on the use of the deblur plug in, its purpose is to denoise the sequencing data (probably pre-processed for merging into a single sequences and quality filtering), and is not for taxonomy assignment.
Among the deblur output you will find an artefact including the representative sequences, and it is this one that should be use for the taxonomical assignment step wit. Again, I think
it would be useful to work on the “Moving Picture tutorial” even if is not strictly on fungi (https://docs.qiime2.org/2020.2/tutorials/moving-pictures/).