sale_order_ids in your if conditions

if lead.sale_order_ids.is_primary_quotation

is not a single Sale Order, because 

1. sale_order_ids = fields.One2many() - thus either no record, one record or many records
2. you've probably never told sale_order_ids to be one specific record, i.e. by applying an actual search domain

See the domain attribute for One2many https://www.odoo.com/documentation/18.0/developer/reference/backend/orm.html#odoo.fields.One2many or compute the field.

Apart from that I don't think much can be said since your source doesn't really add up - to me at least. is_primary_quotation implies to me that there should be a single primary Sale Order only - but primary in regard to what? The Lead, a Customer, ...? You probably want to apply some logic that actually enforces is_primary_quotation to be possible to be set only once for any given sale.order linked to a crm.lead, i.e. by checking in create() and write() of sale.order whether any lead_id.sale_order_ids.filtered(lambda so: so.is_primary_quotation) is there already.