In this picture, the mock-up of project 21635 "Sarsar" was presented at "Army-2022"; 76 mm caliber gun AK-176MA, 3M-47-01 Gibka-R close-range air defense system, two UKSK (16 launch cells in total), Pantsyr-M.
I'm not sure that this ship from the picture would have anti-submarine weapons, but I think it is necessary to install the Paket-NK system. Anyway, the Russians have developed the anti-submarine system "Otvet" which is launched from UKSK. Therefore, I am of the opinion that these ships would have anti-submarine weapons.
With 16 UKSK, these ships would have far more powerful anti-ship capabilities, as well as the ability to strike with cruise missiles - which the project 20380 corvettes do not have (they don't have UKSK). Moreover, these ships with 16 UKSK missiles have twice the arsenal of the project 20385 corvette (as well as project 11356 frigates) and on a level with the first 4 frigates of project 22350.
On the other hand, these ships would certainly have a smaller navigation radius than the mentioned corvettes, as well as weaker anti-aircraft weapons. Anti-submarine weapons also remain questionable, although I'm sure that the installation of the "Otvet" system would solve that problem + sonar in the front of the ship.
I have written about this before and the Russians have obviously worked on this plan again and it is obvious that there is also a desire to realize the project. Here is the text about it..
Small missile ships of the "Buyan-M" project decided to strengthen to the level of corvettes and frigates
June 29, 2022, 13:49
Text: Dmitry Zubarev
Russia is developing an enhanced version of small missile ships of Project 21631 (code "Buyan-M"), after which they will come as close as possible in terms of displacement to corvettes, and in terms of strike capabilities - to frigates, a source in the military-industrial complex said. “At the upcoming Army-2022 forum, the state customer plans to consider a modernized project of the very successful Buyan-M project. It is planned to increase the number of universal launch cells for the main range of ship-based missiles at least twice and to strengthen the air defense of the Pantsyr-M ship. Accordingly, the displacement of the ship will also grow, ”a source told RIA Novosti.
According to him, the ship will remain in the "river-sea" class, which will allow maintaining the ability of operational maneuver between theaters of military operations along inland waterways, and due to the increased displacement, seaworthiness in open waters will increase.