Blocking [M]oderns users is tricky because you can't select just a [M]odern toggle, but you can flip settings around to basically remove them.

Go to your Matchmaking settings, then under the Regions & Filters tab you can select the types of challenges you're looking for. In order to filter out just Modern you have to go down to the Controls section, and in the submenu that's labeled "Buttons and Styles" or "Controls" (I forgot which it is I don't have the game open in front of me, lol).

From here you can't directly select [M]odern but you can filter them out if you toggle the following settings:

• Allow use of Enhanced Macros (Toggle: OFF)
  
• Allow use of Quick-Assist Combos (Toggle: OFF)
  
• Allow use of Bluetooth Controllers (Toggle: OFF)
  
• Allow use of Super Art 1 Enhanced Macro (Toggle: OPTIONAL*)
  
• Allow use of Super Art 2 Enhanced Macro (Toggle: OFF** SEE NOTE BELOW)
  
• Allow use of Super Art 3 Enhanced Macro (Toggle: OPTIONAL*)
  
• Allow use of Specific Character (SEE CHARACTER SELECT NOTE BELOW)

* NOTE ABOUT SUPER ART 1 AND 3:
I usually turn this one off, Super 1 and Super 3 have invincibility and it's very cheap (some would say a cheat CrapCom left in) and not fair when trying to have a fair ranked match. I toggle this to OFF and you want to climb anywhere higher than Gold you will have to toggle it OFF as well or be some kind of god gamer to not get hit by this spam crap.

** NOTE ABOUT SUPER ART 2:
You 1000% have to turn this one completely off, too many of the Super Art 2s in this game are cheap and they don't even tell you what they do. Blanka's for example allows him INFINITY electric balls and without any way to stop it, they are literally unblockable. You have to turn this off. Also by turning off the Supers you will ensure no Enhanced Macro loving Super Spammers will get in the ranked filter.

CHARACTER SELECT FILTER NOTE
[M]odern scrubs usually use the same characters and thankfully with the newest update you can select who you want to meet in ranked. If you toggle these characters off you will see 80% fewer [M]odern matchups in ranked:
TOGGLE OFF: (Luke, Lily, Manon, Marisa, Ryu, Ken, JP, Aki, Rashid, Zangeif, Dhalsim, Kimberly, Jaime, Blanka)

After you have unchecked those options and set the right toggle you can back out of that menu and go down to the Connections/Network settings. There will be something like "NAT Port Status" or "NAT Status" depending on if you have WiFi 6 or Cat5 connection. IF YOU DO NOT HAVE WIFI YOU CANNOT DO THIS NEXT STEP, YOU HAVE TO HAVE WIFI TO BLOCK [M]ODERN PLAYERS PLEASE DO NOT WRITE TO ME ASKING ABOUT THIS STEP IM TIRED OF EXPLAINING IT go to the next menu, next menu, and then skip past the subnet stuff. From HERE you can switch of "Allow NAT Port Transmission Handshake" and then set the setting underneath it (again I forget its something like "Port Opener") to just anything, like 980 or lol or something.

When you start up ranked you should see the filters applied and that will take care of the [M]odern users in ranked.