Your issue looks similar to mine.
I removed MSI when installing Magento 2 - Then after purchasing an ebay plugin we needed MSI - so then I re-installed it - and like you - my "Saleable Quantity" was blank - not 0 - blank.
My product with blank saleable quantity
After a load of googling and looking at other posts - I found I'd f****d the db.
My 'inventory_source_item' was empty - so to fix this I found a post on here:
https://magento.stackexchange.com/questions/294286/after-migration-inventory-source-item-table-is-empty-magneto-2
The SQL provided fixed the 'inventory_source_item' table.
INSERT IGNORE INTO `inventory_source_item` (source_code, sku, quantity, status) select 'default', sku, qty, stock_status from (`cataloginventory_stock_status` as `lg` join `catalog_product_entity` as `prd` on((`lg`.`product_id` = `prd`.`entity_id`)))
^ Important: here 'default' is the source_code of your stock source - if yours is like mine then the SQL should work as is, otherwise change 'default' to 'yourstocksourcecode' ^
My stock sources
but still my "Saleable Quantity" was blank.
Then I noticed the 'inventory_source_item_link' table was empty. I simply inserted 1 row:
INSERT INTO `inventory_source_stock_link` (`link_id`, `stock_id`, `source_code`, `priority`) VALUES ('1', '1', 'default', '1');
and now my Saleable Quantity is there 1 row doesn't have it because its just the grouped product...
My products showing saleable quantity
It's also worth pointing out - after the final SQL I re-indexed to make sure it would be there:
php bin/magento indexer:reset && php bin/magento indexer:reindex