Create a chord progression in B major that has a rather sadder tone.
To create a chord progression in B major with a sadder tone, we can utilize the natural minor chords and the IV (4th) and V (5th) degree major chords, which have a more emotional and tense sound. Here's a suggestion for a chord progression:

Bmaj - G#m - E - F#

1. B major (I): B - D# - F#
1. G# minor (vi): G# - B - D#
1. E major (IV): E - G# - B
1. F# major (V): F# - A# - C#

Playing these chords in this order creates a progression that starts in the major key, but has a sadder and more emotional quality due to the inclusion of the minor and major chords from the 4th and 5th degrees.
your 4th degree chord is not minor ...
but 6th is.
Can you improve your anatole progression with seventh and/or ninth chords ?
Finally can you create tension on the fifth degree resolving to B major ?
For example your fourth mesure should be B7/B7-5# resolving to B7M.
Know can you imagine a melody on this progression ?
You are right, the 4th degree chord in B major is not minor, but major. To improve your anatole progression with seventh and/or ninth chords, you can add the 7th and/or 9th scale degrees to each chord. For example, to make a Bmaj7 chord, you would add the 7th scale degree of B major, which is A#. To make a Bmaj9 chord, you would add the 9th scale degree of B major, which is C#. The formula for adding these extensions is the same for any chord.

Here's a suggestion for a chord progression with seventh and ninth chords:

Bmaj9 - G#m7 - E9 - F#7

    Bmaj9 (I): B - D# - F# - A# - C#
    G#m7 (vi): G# - B - D# - F#
    E9 (IV): E - G# - B - D - F#
    F#7 (V): F# - A# - C# - E

To create tension on the fifth degree resolving to B major, you can use a dominant seventh chord with an altered fifth, such as F#7b5 or F#7#5. These chords have a tritone interval between the third and the seventh, which creates a strong dissonance that wants to resolve to the tonic. For example, your fourth measure could be F#7b5 resolving to Bmaj9.

Here's how it would sound:

Bmaj9 - G#m7 - E9 - F#7b5 - Bmaj9

    Bmaj9 (I): B - D# - F# - A# - C#
    G#m7 (vi): G# - B - D# - F#
    E9 (IV): E - G# - B - D - F#
    F#7b5 (V): F# - A# - C - E
    Bmaj9 (I): B - D# - F# - A# - C#

To imagine a melody on this progression, you can use the notes from each chord as well as passing tones from the scale. A simple way to start is to use the highest note of each chord as a guide for your melody. For example, you could sing or play something like this:

C#-F#-F#-C-E-C#

Of course, there are many other possibilities for creating melodies on this progression. You can experiment with different rhythms, intervals, and embellishments to make it more interesting and expressive.
Thanks, I'll try it.
Okay, enjoy!