Vyxal, 18 bytes

ƛꜝ;5ẇRƛB;kAkd+$İṅ+

Try it Online!

My first attempt at golfing in Vyxal.

Explanation

ƛꜝ;5ẇRƛB;kAkd+$İṅ+
ƛ ;                  Map
 ꜝ                     Is uppercase?
   5ẇ                Split into chunks of 5
     R               Reverse each
      ƛ ;            Map
       B               Convert from binary
         kAkd+       Push uppercase letters joined with digits
              $      Swap
               İ     Index
                ṅ    Join into a string
                 +   Append to the original string

Vyxal, 18 17 bytes

ƛꜝ;5ẇRvBkAkd+$İṅ+

Try it Online!

My first attempt at golfing in Vyxal.

Explanation

ƛꜝ;5ẇRvBkAkd+$İṅ+
ƛ ;                 Map
 ꜝ                    Is uppercase?
   5ẇ               Split into chunks of 5
     R              Reverse each
      v             Vectorize
       B              Convert from binary
        kAkd+       Push uppercase letters joined with digits
             $      Swap
              İ     Index
               ṅ    Join into a string
                +   Append to the original string

Vyxal, 18 bytes

ƛꜝ;5ẇRƛB;kAkd+$İṅ+

Try it Online!

My first attempt at golfing in Vyxal.

Vyxal, 18 bytes

ƛꜝ;5ẇRƛB;kAkd+$İṅ+

Try it Online!

My first attempt at golfing in Vyxal.

Explanation

ƛꜝ;5ẇRƛB;kAkd+$İṅ+
ƛ ;                  Map
 ꜝ                     Is uppercase?
   5ẇ                Split into chunks of 5
     R               Reverse each
      ƛ ;            Map
       B               Convert from binary
         kAkd+       Push uppercase letters joined with digits
              $      Swap
               İ     Index
                ṅ    Join into a string
                 +   Append to the original string