I’ve been playing WoW for a few years now but haven’t tried any “gold making” methods other than running old content for gear, but I haven’t begun collecting mounts and pets to sell, is there a good addon for helping me find mounts and pets to sell on AH? Have a great day whoever reads this. <3
Are you talking about an AH addon that will track pricing on mounts and pets for you to maximize profit? If so Auctioneer or TSM will both do this for you.
Or are you looking for an addon that will tell you what to go farm, where to get it, etc.? If so, nothing that I’m aware of does this. Only research and experience will be able to guide you here. There are tracker addons that will be able to help you find rare spawns when you are out farming, so I would suggest looking into those to make your life a bit easier.
But other than that I would also suggest keeping an eye on patch and expansion notes as far in advance as you can. A lot of times there will be new materials, pets, and mounts that will be highly sought after for a few weeks after the new content is available. For example, you can usually make a killing from selling new ore and herbs within the first week or two of the content, and any new BoE mounts and pets that are introduced will have people salivating to get their hands on. You may sacrifice some player progression for gold in those first weeks, but if gold is your goal, you’ll just have to choose how to allocate your time. 
There’s youtube videos on farming sellable mounts.