Does Unicode display differently in High Sierra and Catalina?

I love to type arrows! Instead of using kluges like --->, I like using unicode arrows, such as ⟶. I found a bunch of them, such as: ← → ➡ ⬅ ⮕ ⮕ ➜ ➞ ⬅ ➔ ⇦ 🡄 ⟸ ⟹ ➙ ➨ ← ⟵ and ⟶ .

But I've found that High Sierra and Catalina render these somewhat differently -- even though all the characters are (I believe) standard Unicode, set in standard "Unicode fonts" that are supposed to be able to render almost all Unicode characters.

Here's what I mean. Below, lines 1 and 3 are screenshots pasted as graphics -- 1 from an old Mac Mini running High Sierra, and 3 from the machine I'm using right now, a recent MacBook Air running Catalina. In between, on line 2, are the raw Unicode characters that were screen-shotted above and below:

1   High Sierra: 

2   Actual characters:

← → ➡ ⬅ ⮕ ⮕ ➜ ➞ ⬅ ➔ ⇦ 🡄 ⟸ ⟹ ➙ ➨ ← ⟵ ⟶ 

3   Catalina:

I'm guessing that most people reading this now will have line 2 match either line 1 or line 3.

Does anybody else see this? Is there a setting on my Mac Mini/High Sierra that will render all those arrows correctly? I'm particularly concerned that the heavy left-arrow and the corresponding heavy right-arrow don't show up all the time (these are the 4th and 5th characters from the left); it's very inconvenient to be able to point forcefully to the left, but not to the right!

Thanks, in advance, everybody, for your help in understanding this puzzle.