Hello @JosG ,
Thanks for contacting NXP Tech Support.
For more information about DSE, you can find it in the Data Sheet. It is mentioned that "PE, PS, SRE, ODE and DSE are supported in the Pin Control register of all types of IO. 5VTol and HD pads support two DSE bits in the Pin Control register of the pin." In the PCRn register, DSE and DSE1 are the names of these two bits. Not all PCRn registers have two DSE bits; some only have one. The details can be found in the Reference Manual. Based on this, the I/O pin diagram structure is easy to understand. The DSE indicated on it includes both DSE and DSE1.
You can also find some useful information in the Data Sheet. For example, as mentioned on page 23, as shown in the following figure:

For a detailed introduction to PCRn[DSE], you can refer to the figure below.

I hope the above information is useful to you.
Best Regards,
Celeste