Your problem is the "Within-group aggregates" problem, see discussion under that heading at
https://www.artfulsoftware.com/infotree/queries.php.
Your best bet might be a variant of #5 in the above list. It's not clear from your query whether you want the lowest minimumordrprice or the lowest price; assuming the former, you query might be ...
select p.name, s.name, s.minimumorderprice, h.*
from product as p
join product_has_supplier as h on p.product_id = h.product_product_id
join supplier as s on h.supplier_supplier_id = s.supplier_id
where p.product_id = @productid and h.isparallel = @isparallel
order by s.minimumorderprice asc limit 1;
Comma join syntax has limitations. Explicit join syntax is easier to write debug & maintain.
Limit N to see the N best N prices.