Hello @ayesha_khalid ,
Basically, there are some constraints for lengths of the attributes.
e.g : meta_keyword,meta_title and meta_description
meta_title has the type varchar and is stored in the table catalog_product_entity_varchar. The limit on the value field of the table is 255.
meta_description and meta_keywords have the type text and is stored in the table catalog_product_entity_text. The limit on the value field of the table the limit of the text fields in mysql. For text is "L + 2 bytes, where L < 216".
Please refer for Data Type Storage Requirements : https://dev.mysql.com/doc/refman/8.0/en/storage-requirements.html
NOTE : I think, you shouldn't use large meta keywords and meta descriptions.
A meta description of 255 chars is more than enough.
As for meta keywords, you should ask a SEO expert on this, but I'm sure the recommended number does not go over 10.
If my answer is useful, please Accept as Solution & give Kudos.
Thanks!!
Binod Yadav
If my answer is useful, please Accept as Solution & give Kudos