What European alphabet has the most letters?

I'll take a stab at this one:

The modern Bulgarian alphabet has 30 letters.

The Modern Bulgarian Period started in the 15th century, but the modern literary language, which is quite different from Old Bulgarian, formed only during the 19th century.

Until that time St. Climent's original Cyrillic alphabet, containing 44 letters for 44 sounds, had been used; however, by the 19th century the Bulgarian sound system had changed dramatically and contained fewer sounds.

That necessitated an alphabet reform which reduced the number of letters used from 44 to 32; this modified alphabet was used until the Orthographic reform of 1945.

Most letters in the Bulgarian alphabet stand for one specific sound and that sound only.

The Anglo-Saxon Futharc has 34

https://en.wikipedia.org/wiki/Anglo-Saxon_runes

The Czech alphabet has 42 graphemes (which could be called letters).

https://en.wikipedia.org/wiki/Czech_alphabet

The Hungarian alphabet.

https://en.wikipedia.org/wiki/Hungarian_alphabet

One sometimes speaks of the smaller and greater Hungarian alphabet, depending on whether the letters Q, W, X, Y which can only be found in foreign words and traditional orthography of names are listed, or not.

There are 44 letters in the (greater) Hungarian alphabet.

The longest European alphabet is Slovak alphabet.

https://en.wikipedia.org/wiki/Slovak_orthography#Alphabet

Slovak alphabet has 46 letters which makes it longest European alphabet.

The Latin-derived Slovak alphabet, which has 46 letters, is the longest European alphabet.

https://en.wikipedia.org/wiki/Alphabet