I started growing plants since covid - so a novice :) I noticed that the leaves from the mint plant were turning rusty brown. Initially thought that it was just regular life cycle, but now I'm noticing them on the other leaves as well. Please help!
As you are growing this indoors, that makes it more likely the plant has a spider mite infestation, which is what it looks like rather than Mint Rust (which is the fungal disease). Spider mites on plants indoors are fairly common because the air is much drier and hotter than outside, and if you are using grow lights, that would make it an even more hospitable environment for them. All the time it's growing inside, mist it frequently to try to keep the humidity up, after you have taken steps to clear the infestation.
Because this is an edible plant, you are restricted in terms of pesticide treatments - spraying hard with water will clear many of them, but will need to be repeated frequently. Otherwise use a plant based insecticide, such as one based on pyrethrum or rosemary oil - most insecticides which are intended for use on edible plants should be fine. Make sure you spray the whole plant, including stems and backs of leaves. Further info here https://dengarden.com/gardening/Mint-Pests
Check all your other houseplants - spider mites are rarely only on one plant indoors, unless it's in a room on its own.
The more you pick the leaves, the fresher your leaves will be on the mint. Yellow leaves is either a sign of lack of sunlight, water or other nutrients. Or may be they have just aged. Better pick them regularly and enjoy fresh. Or dry them to use later or make some spicy mint powder (indian way) that can be used as a condiment or sprinkled & eaten on toast.