In ruby-acts-as-taggable-on 6.5.0-2~bpo10+1 package has already been the problem fixed. In ruby-attr-encrypted has helped me the following workaround directly in the source code (taken from ruby-acts-as-taggable-on's fix):
Line 84 in /usr/lib/ruby/vendor_ruby/attr_encrypted/adapters/active_record.rb #set_attribute_was(attr, __send__(attr)) if value != __send__(attr) if ActiveRecord.version <= Gem::Version.new('5.3.0') set_attribute_was(attr, __send__(attr)) if value != __send__(attr) else unless #{attr}_changed? @attributes[attr] = ActiveModel::Attribute.from_user(attr, __send__(attr), ActsAsTaggableOn::Taggable::TagListType.new) end end