Shimano Deore as Gravel Bike

Assuming your shifters are SL-M5100

• https://bike.shimano.com/en-SG/product/component/deore-m5100/SL-M5100-L.html
• https://bike.shimano.com/en-SG/product/component/deore-m5100/SL-M5100-R.html

Then the product matrix at https://productinfo.shimano.com/#/com?cid=C-432&acid=C-435 says no.

Sadly the "gravel bike" specific groupsets are based on road bikes so have road bike pull, and deore is MTB pull.

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Your solution might be to replace the shifters with ST-RX810-R and ST-RX810-L which is 2x11 speed GRX, and the rear mech with RD-RX800-GS or RD-RX810 or RD-RX815, and the front mech with a FD-RX810-F or FD-RX815.

This also depends on if you have cable or hydraulic brakes.

Store the take-off parts in case you want to revert later.

Unfortunately 11 speed MTB and 11 speed road have different pull ratios.

You could use this adapter/converter: https://www.wolftoothcomponents.com/products/tanpan

It should allow you to keep using your existing rear derailleur and cassette.

I have this MTB with Deore M5100 groupset (2 x 11 speed) and I want to convert this MTB to gravel bike. Is there any brifter compatible for this series?

Unfortunately, the times are not good for doing flat bar to drop bar conversion.

I did such a conversion on a bicycle with V brakes and 8 speed drivertrain. I only needed bar-end shifters and drop bar V brake levers, plus the drop bar of course. Back then the times were different. Shimano wasn't making everything incompatible between drop bar and flat bar on purpose. Yep, Shimano didn't sell drop bar V brake levers but third party manufacturers came to the rescue.

There is no brifter and no bar-end shifter (or downtube shifter) compatible with the Deore M5100 rear derailleur cable pull ratio. Unless you like friction shifting in which case it might be doable with bar-end or downtube shifters (but due to the long cable pull you might find the range of the friction shifter isn't enough for all the gears).

As already noted in other answers, there is no compatible unit. The pull ratio is different.

However, given the typical prices of brifters and derailleurs, I think it would be better to buy a new 11-speed derailleur that is compatible with your new brifters - such as the Shimano GRX.

It will be better than some extra units for pull ratio conversion.

The front derailleur might be necessary too, but it is even cheaper.

There are no Shimano brifters that are 2x11 compatible, but Microshift manufactures some. I use a Microshift SB-110 (1x11) and a bar-end shifter for a drop-bar 3x11 setup with an XT rear derailleur (RD-M8000) and XTR front derailleur (FD-M9000) with no issues.

Here is Microshift's product page for the SB-110: https://www.microshift.com/en/product/sb-m110/