Maximum output pin current for 3.0 V LVTTL with 2.5 V supply

The question title " 3.0 V LVTTL with 2.5 V supply" sounds still confusing. 3.0V LVTTL specifications are for 3V rather than 2.5 supply. You won't find a specification for output current with wrong supply voltage. It can be derived if you understand the relation of current strength settings and supply voltage, but that's beyond supported specifications.

Still not sure what you mean with "maximum output pin current"? Under which conditions? Which current strength settings?

In any case you should consider that with higher current strength, the actual output current may be above maximum rating of +/- 25 mA so that the output driver might be damaged.

For a complete specification of output characteristics review MAX10 Ibis files. https://www.altera.com/support/support-resources/download/board-layout-test/ibis/ibs-ibis_index.html