Is Arcana the only profiency in 5e that locks something behind the *skill* profiency system?

Question

What opportunities are locked behind skill proficiencies?

I keep trying to look through things as soon as I learned that because of XGTE you can only craft scrolls / magic items if you have proficiency in Arcana. And no matter where I look I don't see anything else locked off because you aren't proficient in the skill. I would like to know if are there things locked off that require proficiency in a skill?

For clarification, I'm asking for things you can't do without the proficiency not ones where it makes it much easier to do so, i.e., you can still stabilize creatures without medicine proficiency but it is harder to do so.

As an additional clarification, I'm not looking for things related to other proficiencies, including weapons, tools, and armor.

What I found out during research

Here's what I do know about the different skills:

Athletics- Grappling, avoiding grappling, and long/high jumping but it doesn't stop you from doing it if you aren't proficient

Arcana- The only one which stops you from making spell scrolls and magic items without it

Acrobatics- Preventing grappling, random item checks, and random dm checks

Animal Handling, Deception, Intimidation, Performance, Slight of Hand, and Stealth- Are checks that affect npc's but to do those checks proficiency only increases your odds to do so

History, Investigation, Insight, Nature, Perception, Religion, and Survival- Are just random checks for info but to do those checks proficiency only increases your odds to do so

Medicine- Helps stabilize creatures but you don't need to be proficient in it to do so

I'm not saying don't take prof in these skills if it's what your character would do, but I'm just wondering if I'm missing out on info like I did about spell scrolls and magic item creation.

Answer 1

Skills vs. Tool Proficiencies

As you say, nearly all of the skill proficiencies function to improve a character's chance of doing something, but not to permit that thing.

Proficiencies that are 'gatekeepers' are more likely to be tool proficiencies, not skill proficiencies. As the PHB crafting rules explain (187):

You must be proficient with tools related to the object you are trying to create (typically artisan’s tools).

However, there is no artisan's tool associated with magic item crafting, and the core rules (DMG 128, 129) do not list a required tool proficiency to make magic items - only that the crafter be a spellcaster.

As NautArch points out, the requirement of proficiency in Arcana for magic item crafting proficiency is not a core rule, rather it is an optional rule that was added in Xanathar's. Given how Xanathar's expanded the rules for tool use, it is odd that it chose to tie magic item crafting to skill proficiency in Arcana, rather than to invent something like an 'Arcane instruments' tool proficiency.

Answer 2

Tool Proficiency

From Xanathar's Guide to Everything (optional rules)

Item crafting requires appropriate tool proficiency

Brewing health potions requires herbalism kit proficiency

Tool proficiency is required to unlock some benefits of some tools

Answer 3

The requirement of the Arcana proficiency to create Spell Scrolls is unusual. The PHB clearly states that by default proficiency is not required. If a skill proficiency applies the PHB says (emphasis mine):

[...] proficiency in a skill means an individual can add his or her proficiency bonus to ability checks that involve that skill. Without proficiency in that skill, the individual makes a normal ability check.

Even for armor, proficiency is not mandatory although the penalties are so large that it's probably never worth it to wear armor if not proficient.

The downtime activities from XGtE are all optional rules! All the crafting activities require a proficiency, although in all other cases (Crafting an Item including magic items) it's a tool proficiency. For magic items Arcana proficiency can replace the tool proficiency but either of the two is sufficient. If Spell Scrolls worked analogously they would probably permit either Arcana or Calligrapher's Tools but for unknown reasons this is not the case.

Rulings

While this is not RAW, I know that many GMs require proficiency for certain tasks. This is reasonable although it is probably best to decide this on a case-by-case basis. I.e. if a player proposes a course of action that seems like it would require a high level of competency that the player doesn't have.

Removing the requirement for creating Spell Scrolls or also allowing Calligrapher's Tools proficiency would be equally unproblematic given that only known or prepared spells can be transcribed.