Learn Hardcore German: Solche starken Figuren beeindrucken viele Leser, besonders Jugendliche. - Such strong characters impress many readers, especially teenagers.

Solche means such ... / such ... as these/those and points to a type of thing, often with a demonstrative feel: Solche starken Figuren ≈ such strong characters (like these).

So on its own usually means so / that / this ... (degree) and focuses more on how strong they are:

Solche starken Figuren – such strong characters (of this kind)
So starke Figuren – characters that are so strong (very strong)

So solche classifies the kind, so emphasizes the degree.

Why is it solche starken Figuren and not solche starke Figuren?

Because of adjective ending rules after der‑words (words like dieser, jener, welcher, solcher).

Solche behaves like a der‑word.
After a der‑word, adjectives take weak endings.
In the nominative plural, the weak ending is -en.

So the pattern is:

solche (der‑word form for nominative plural)
starken (weak adjective ending -en in nominative plural)
Figuren (plural noun)

Therefore: solche starken Figuren, not solche starke Figuren.