I have been playing D:0S2 and I think their combat system is similar to the D&D combat system without being exactly like it. It will have to be tweak more to be fully in line with the D&D 5E combat.
How so? D&D combat rules are about
initiative and
rounds and
spellcasting time and
weapon speed and the like. Actions are initiated at your initiative but sometimes maybe completed only at a later point in the round or at the end of the round.
Characters can even have the same initiative and thus act simultaneously. A
ctions can be carried over into a future round depending on time needed for that action to complete. And as such, actions are subject to interruption.
The D:OS system has none of these things. In DO:S everything a character does happens within their turn and are fully completed and resolved within their turn. Then that character is completely done, and it is the next character's turn. Things are very strictly compartmentalized and sequential in a 'per turn per character' structure. These are radically different systems loosely lumped in together as "turn based" systems.