Technically the ij is a digraph and sometimes a ligature. Although computer keyboards have never really supported that but some mechanical keyboards for typewriters used to. Most modern Dutch people would simply be typing an I and a J and wouldn't necessarily know that they need to also capitalize the J at the beginning of a sentence (Ij would be incorrect). Not a lot of words start with that but some place names do.

The Dutch keyboard layout is effectively US international. There are no special characters that that keyboard supports; including all the accents/modifiers we inherited from French, German, etc. Spelling without those is now correct.

This is something that has evolved over the last decades. In the eighties, people would memorize the character codes to produce letters with those. I remember having a card with the right key combinations for word perfect. This is not a thing anymore. People just skip it and the grammar and spelling rules were actually modified to not require these anymore in most situations.

Funnily enough, the Y, is not commonly used in Dutch and usually referred to as the Greek IJ but pronounced the same way.