How would you adapt these combat mechanics for D&D? https://cogentroleplay.com/

I'm making a campaign where it's mostly physical combat with only a little magic available, though there will still be large ritual spells, siege weapons etc to fight the couple gargantuan monsters that might appear during the campaign. Really like how this works, and I think it wouldn't be too hard, just wondering if there's anything weird or troublesome that sticks out.

I’d say that a good first step is to look into the alternative actions for combat because they’re honestly semi under used, I’d also reviewing flanking and maybe reworking grappling along with also promoting subclasses that help combat like master mind for helping as a bonus action or battle master for there cool maneuvers if you intend for a nitty gritty steel on steel like campaign.

for siege type creatures and all that I would give all your building health, determine HP for the building and going below half could make the structure unstable (my take on it you can make your own but give your building health), along with that one thing that will help engage your character with siege combat or warfare let your players roll the damage for firing siege weapons, a dm I had did this once for a siege defense and it was fun hearing how many of the enemies we downed with our roll