It’s not so much that kanji become more difficult, even though they do occasionally have a lot of strokes like 警 or 懸.
What’s harder is when they have vague meanings, rather than easy concrete ones. Or when they are only different in small ways from other ones you know.
照 - illuminate
昭 - shining
招 - beckon
紹 - invite
召 - call
沼 - bog
Here you can see the combo of similar meanings AND similar appearances.
Though, lol, “bog” feels like the odd man out.