amoghdesign I now had some time to take a closer look at your icon shop on Iconfinder and I am ready to give a well-informed answer to your question.
I have looked at your monthly earnings from when you joined Iconfinder and until now. It is true that your earnings have decreased as compared to some years ago.

2017 and 2018 were golden years for you, in terms of earnings. That peak in October 2018 is for a custom icon job, which really made a difference for you that month.
I also looked at how many premium icons you have been adding per month since you joined Iconfinder. I see the icons have a very similar trend to your earnings.

The first 3 years, you have added a considerable amount of icons (with peaks in September and November 2017). The next 3 years, 2018, 2019 and 2020, the number of new premium icons you added was modest in comparison - especially in 2020.
**Tip 1: Quantity when accompanied by a certain level of quality is related to earnings.** This ties into the 1) consistency that customers are looking for and 2) the novelty factor.
First, for the consistency, customers rarely buy just 1 icon and they care a lot that the icons match each other. Having large and comprehensive icon families will attract customers.
Second, adding new icons is important for staying new and fresh and also to being there at the right time. Design trends change all the time and icons start to look outdated after a while. Not only this, but they also are also used by more and more people. For example, Christmas icons from last year might be good, but they have probably been used for last years' marketing material. About timing, staying up to date with events is crucial so that you anticipate what exact icons people will need and when (for example, the US presidential elections, for which you were very quick to create icons and which have been selling very well).
If the icons are especially good, that can give those icons and yourself a huge exposure. They can be featured as staff picks on Iconfinder and they get posted directly on Pinterest and sent to customers in recommendation emails and they are also included in searches when customers use the Staff picks filter. This post explains everything about Staff picks: https://forum.iconfinder.com/d/201-all-about-staff-picks.
Tip 2: Fix the tags of your icons.
First, having good tags is important because that is how customers find your icons. It is a good idea to review tags from time to time (remember to always keep them between 2 and 7) and pick them using the search data that we share in the designer reports.
I can see that you have 62 icons with more than 7 tags each. This lowers their rank in the search results considerably because the algorithm punishes tag spamming. The same for the 39 icons with less than 2 tags - customers really have to type in the exact keyword to find your icons and that lowers these icons' chances of being discovered. This post explains tagging: https://forum.iconfinder.com/d/162-improve-your-tags.
Tip 3: Pay attention to what sells most on your icon shop.
You can see this in sales analytics. I've got the list of the 100 most downloaded icon sets from your shop, which can be very interesting to look at and learn from: https://docs.google.com/spreadsheets/d/1riZ1sxCxzwNpnRriTw3huLwl29Qd0nc7XhZoEVdgzQs/edit?usp=sharing. The top selling one is this timeless glyph set.
Tip 4: Get known
When I mentioned your forum post here to the Iconfinder team, the team did not recognise your designer name nor could tell what your style is. It seems almost like you have been hiding, even though you have been selling on Iconfinder for 5 years. This is the last reaction you would want people to have when you mention your icon business. Ideally, you want to be remembered and for people to know your icons. Part of it is choosing a good name for your icon shop. Another part is to promote (and never stop promoting your work). The top seller icon designers out there are known by everyone and they have each a particular style that can't be confused with others' work. About promotion, there are so many ways to do this: use all the platforms you can (Instagram, Dribbble etc.), run ads, do giveaways, have landing pages where you present icon families, reach out to people.
Tip 5: Invest time in doing quality work and in developing your unique style
Standing out is crucial when you are competing in a large marketplace. Apart from being promoted among the Staff picks on Iconfinder, unique and beautiful icons are recognised and remembered and compete at a higher level than the rest of the icons. It is worth it to go a step further and be more daring, playful, rebellious when designing.
I looked at your icon families and I can give some examples of what works and what doesn't.
The Claro family is nice, yet not very distinctive from other icons out there. It has a basic, correct feel to it, can easily be imitated, and we can't see your personal touch in it.

Same goes for the Dual Tone:

One recommendation is to stop investing into Badge icons - they are not selling:

We also don't recommend putting more time into this style because it also does not sell well.

With the Doodles family, you are on a good path. The icons a nice and cute and there are not many people doing this handdrawn style, so you're tapping into a niche. Great move!

Pushing some boundaries in icon design is very hard work, but highly rewarded.
I hope this answer has helped you! I am here in case you have any questions.