Verified answer

Ь softens the consonant before it. If before a vowel, it also separates the consonant from the vowel and inserts "j" sound.

Ъ, unlike its use in Russian, is usually an indifferent vowel (like when you pronounce "further"). But in your example, its function is exactly the same as in Russian - it separates the vowel from the preceding consonant and inserts "j" sound without softening the consonant.

It wouldn't make sense here to use a "proper" letter. C- is a prefix; the ъ character separates the prefix from the root audially. It wouldn't be there if the next character weren't a soft vowel.

i'm no longer russian yet PITY am conscious of slavic langs so ? is like english "uh" like you pronounce "lower than" or united statesor ? is softening the letter before it like in spanish sueÑo or portuguese carvalHo a similar function because the spanish n with tilde and "h" in portugese

It's mostly used to mark the schwa sound.

Maybe here it has other uses like Съединението to mark the C as hard.