you probably want to desterilize your json into an object

and then what?

depends if you want to use something like dapper or efcore, or if you just feed the data by hand into some sql client

at work we serialize it to protobuf

so it's just some bytes

pretty compact

Can you then compress the protobuf output to make it even smaller?

I would try not compress the JSON data. Insert it as it is as JSON. SQL server has built in JSON support to query that data. If you compress the data before inserting it, SQL server is not able to query information out of the JSON data structure. It can only retrieve the full compressed blob.
This fully depends on your requirements.
Example (from https://learn.microsoft.com/en-us/sql/relational-databases/json/json-data-sql-server?view=sql-server-ver16):

SELECT Name, Surname,
  JSON_VALUE(jsonCol, '$.info.address.PostCode') AS PostCode,
  JSON_VALUE(jsonCol, '$.info.address."Address Line 1"') + ' '
  + JSON_VALUE(jsonCol, '$.info.address."Address Line 2"') AS Address,
  JSON_QUERY(jsonCol, '$.info.skills') AS Skills
FROM People
WHERE ISJSON(jsonCol) > 0
  AND JSON_VALUE(jsonCol, '$.info.address.Town') = 'Belgrade'
  AND Status = 'Active'
ORDER BY JSON_VALUE(jsonCol, '$.info.address.PostCode')

SQL server also has build in support for compress/decompress. Check article https://techcommunity.microsoft.com/t5/sql-server-blog/storing-json-in-sql-server/ba-p/384576
What is your requirement for compression? Faster transport, DB space, ...?

@844594574906228736 db space

I achieved half the size using brotli and it works for json input and output

Seeing if I can make that even less

so is db space a major concern?

@296666311688454144 well I’ll be dealing with large json files soon so yeah

you can just store the files too

on disk

it's already really small

many times smaller than json