Unless it’s very butter-forward cookie like shortbreads vegan butter works just fine.
D1 is vegetarian and typically bakes vegan recipes for cookies, brownies, waffles, pancakes, etc.
She uses only vegan butter and uses chia seeds (soaked in warm water until gummy) to replace eggs. Try chia if flax is giving you off flavors. Chia substituted recipes will have less “lift” so may turn out denser than the original recipes.
Her vegan brownies, from the cookbook below, are excellent , though you have to be very vigilant when baking them because if you overtake by even 1-2 minutes, the brownie is very dry and doesn’t keep at all. If in doubt underbaking is better.
Her recipe involves almond butter so it may not work if anyone has nut allergies.
This is her go to cookbook: The Joy of Vegan baking
If you want cake recipes–look for olive oil cakes. Olive oil subs for the butter and keep the cake very moist. There are many olive oil cake recipes that don’t use eggs. (In fact a hack professional bakers use is to sub 1/2 vegetable oil for butter when baking cakes to make the cake stay moister for longer.)
You may want to take a look at this site: