I'm afraid I don't have a good answer for you. Lookup fields and multiple-value are specific features to MS Access, they are not well-exposed through the MS JET driver that Microsoft makes available for other applications (like Tableau Prep) to connect to MS Access databases.
In my prior work with MS Access (and Tableau Desktop) I ended up doing a lot of joins to replicate the results of lookup fields.
Multiple-value fields are something that MS came up with to make life easier and they work great as long as you're in an MS-only environment, however for tools like Tableau Prep and Tableau Desktop that approach data more like a database does they are more challenging. In Prep you'll likely need to do a split to parse out the multiple-value field to multiple columns, then a pivot on those results so you end up with a normalized data set with one record per value.
Thank you so much Jonathan, that’s a very thorough and clear explanation. I get it.
It looks like with lookup fields we should really stick with access only, because I tried with power bi (from MS also) and the problem is the same.
I’ll have to workaround it.
Thank you again,