Welcome to the community, @Per_Hylten!
It depends on what you mean by “access”.
If it’s just a read-only view of your data, you could manually create 300 different filtered views and then share those 300 different view links of your system with your 300 different clients.
However, even though that’s “technically possible” with Airtable, nobody really wants to manually create & manually maintain 300+ different views. That would be extremely tedious and time-consuming and frustrating. (And there might even be an internal limit on the number of Airtable views you’re allowed to have… I’m not sure if you’re even allowed to have 300 views.)
So what you really want is dynamically-changing views of your data, based on whoever is logging in to access your data.
Unfortunately, this is not possible using Airtable on its own. This is only possible with Stacker or Mini Extensions.
Furthermore, if “access” means that you want users to VIEW & EDIT their data in your system, this is not possible at all with Airtable. This would REQUIRE the usage of either Stacker or Mini Extensions.
Hope this helps!
p.s. If you have a budget for this project and you need to hire an expert Airtable developer to help you integrate Stacker or Mini Extensions, please feel free to send me a private message or contact me through my website at ScottWorld.com.