I like this one very much:
https://www.shutterstock.com/de/pic-68874208/stock-photo-taj-mahal.html?src=MsUAPl8KDnafjnTEbUDheg-5-2
But there is a gazillion of great photos from Taj Mahal.

You're probably a few years too late. To earn significant money in microstock a photo should get to the top of search results (most popular on SS, in the good old times they called it Best Match at iStock). It is much more difficult to achieve now, than it was a few years ago, because there are millions and millions more photos in the pool. And with time it should get even more and more difficult.

You must answer it for yourself, if time spent on microstock is time wisely spent. The future for individual photographers doing microstock is not looking good. Some people moved on to do better things, but their portfolios stay in the pool.

Not sure how to use your images.
Nice pumpkings but bad background (wall).
pic-502401679

Yeah, that's slightly off-putting. People might not have the know-how to straighten it themselves, so they might overlook it. Try not to give buyers any reasons not buy your images.

...Is 100$ a month viable via microstock photography these days. If not, what (if any) are the alternatives.

If yes, what would you suggest I do to improve my performance ?...

$100 a month from SS alone is not hard to reach, but you do need to think about images from a buyer's perspective - what could someone do with the image? Look at ads, any corporate marketing materials you see, web sites for various types of businesses large and small. How many images you need very much depends on quality and subject matter - out of the way locations and random objects will require much larger portfolios than high-demand subjects.

Shoot at least horizontal and vertical of anything you think is useful (many uses prefer horizontal but books will typically look for vertical); think about copy space around the subject, think about closeup and wide views. Make sure you get the details you need to keyword fully and accurately. For anything shot outdoors, try to pick times of day when the light is good.

Regarding keywords, your images need work. I saw an image of Bath Cathedral that had Canterbury as a keyword, oysters that had mackerel as a keyword, images with both Nagasaki and Tokyo, octopus which had moray and mackerel, but not octopus; all sorts of images with keywords for things I didn't see in the image. I'm assuming you're doing cut and paste without editing  - don't do that sort of spamming; it won't help your sales and some sites may suspend you for doing it on a regular basis.

Some things that seem boring - many home maintenance projects - have a good market as lots of companies in the business need stock images for their work. Things you'd never sell prints of can be solid subjects for stock photography. Search for things you're thinking of shooting on one of the major sites and see what sort of competition there is - and is there anything you can bring to the subject that isn't already covered.

Good luck

Asking for a critique from MicrostockGroup May have some value to you but no one here will be able to tell you what you need to do to achieve your goal.

You shouldn't need a critique from this site though, you should be your own worst critic already. You're not. If you could see your own work objectively, you wouldn't need anyone to tell you your Taj Mahal pic was crooked, you would have already seen that yourself and fixed it.

Learn to see your work as others do (not your friends and family either). Then take your best shot and compare it to a similar shot on SS. If it doesn't hold up, then you know what you need to do.

Put a focus on commercial work that sells. Every contributor who has a camera take everyday and travel photos. That stuff has been done over 10000 times by everyone else.

Look at public billboards, advertising and websites and see what type of imagery they use. Those are the stuff that sells, not everyday photos like leaf textures, rock textures, trees and generic urban landscapes.