Is it possible to add a select tickbox to the PXSelectReadonly View, and make it available for the user to tick items from the grid?
I tried adding it but it is always disabled. I can understand that this is because the PXSelectReadonly does not allow updating so everything would be read-only, but is still a way to achieve this, or do you need to use a standard PXSelect view, and then disable everything except the select tickbox?
Difference between read-only and regular data views is explained in detail in the Merged and Read-Only Retrieval Modes section of the T200 training class, which can be downloaded from Acumatica Open University). Read-only data view types do not contain or execute any UI presentation logic and, in terms of presentation, logic are identical to regular PXSelect types. Have you tried enabling Select field in the RowSelected handler or BLC constructor? It would also help if you update your question with source code of your DAC and BLC.
Update based on the comment from Joseph Caruana below:
Besides the difference in data retrieval modes, PXSelectReadOnly data views now make entire grid read-only ignoring all field state configurations made at the runtime via PXUIFieldAttribute.