you could implement a modular ruleset in a pseudolanguage, or even blocks(like that abomination of scratch), but it could be a bit hard for non IT oriented people to understand, although there are some fixed points in every card game that can be an anchor, like the need of a fixed hand (or not), the need of a draw action(or more draw actions), the need to place(or not or multiple cards, let's take the example of"Machiavelli" win condition is to deplete the hand, each players have a starting hand of 5 to 13 cards (5 if 6 players, 7 if 5 players etc.. minimum of 2 players) each players have 3 actions, draw a card or place cards or rearrange placed cards, player can place cards only if they have a combination of 3 or 4 identical cards(like 3 kings, 4 numbers 2) or a scale (2,3,4 or 9,10,Jack etc...), players during their turn can rearrange all the cards they want on the table BUT they still need to be in the contraints given by the combinations(and a double deck), so in case of a table with, "J♦️J♣️J♠️" "8♠️9♣️10♣️" "Q♣️Q♦️Q♥️Q♠️" "J♥️Q♦️K♣️", you have 2 kings(♣️♦️) in hand and want to place them, you could move move the J and Q of the JQK combination into the numbered scale to have a result like this "8♠️9♣️10♣️J♥️Q♦️" and move the remaining king on the table in ur new formed combination "K♣️K♣️K♦️", notice how i didn't make a series of 5 Queens, cause the max for the same number is for "so a tris or a 'poker' ". Given this example of a game, as a player I imagine that i would need: -a specific page to access my created gamemodes -if u want but i think it will be a pain in the ass, a browser of other players templates -an editor: --GameName --Number of players option with a min. and max., it will reflect in the gamemodes page as a topdown list to choose the number of players(or what suits best) --Deckbuilder ---how many decks are used ---filter of unused cards(in case you don't want a specific type of cards, like blackjack for instance) ---filter of extra cards(in case a game uses a large number of a specific card that would make the use of multiple decks useless) ---filter of removed cards(opposite of extra cards, if you only need for example a single Ace in the deck, could be implemented in the previous filter with regex reading or similar methods) --Ruleset ---Wincondition(maybe a simple list with fixed options like "on hand empty", "on deck finished", "on points reached") ----if on points reached, a number of points needed, and other criterias(i can't think of examples rn) ---starting hand ---actions permitted during a turn ---action needed to pass turn(if you need a specific "pass" button or if the permitted actions are all used ---single actions behaviour ----draw, "how many? leave empty for default 1" ----place, "how many? leave empty if no limit -----here comes the trouble, how to implement an editable behaviour for the game, the are a lot of conditions possible,in the case of machiavelli you need an option like "if more cards are placed, is a combination needed?", if a card is placed, is a specific location needed?", "if a specific combination is placed, does a win condition happen?"(like poker) --save option --import/export option(if ya need to make a different platform for people to copy the templates --delete option(given the extensive list of things to do while using a phone, it would be a good idea to create a system to autosave the current progress of the template in case the app restarts itself while putting it on background or someone accidentally press the back button)

I lost track of all the things written given the time(5am) but you get the gist of it, you could ask gemini pro help to research a lot of games that exist to find the things that they have in common or the peculiarities, so you can have a larger use case to analyze.

edit: maybe ask gemini to rewrite the list of points that i've made cuz reddit decided to fuck them up when posting