Hi @mari_lopes,
I've been able to construct a SILVA classifier just fine using usegalaxy.edu. Basically, on my laptop, I used RESCRIPt to download and curate the SILVA 138.2 database. Then I uploaded the sequence and taxonomy files to usegalaxy.edu and trained the classifier using qiime feature-classifier fit-classifier-naive-bayes ... (it looks like this function it is currently using QIIME 2 version 2025.4). Perhaps that'll work for you?