Attempting a Scribe action on a Scroll of Fireball (so 3rd level), with a level-3 wizard with INT 18 (+4) and Intelligence Arcana +6, is not possible, hovering the mouse on the greyed-out option justifies that with "The spell level is too high".

Even if the spell level is higher than the caster level, there is still a chance of success with a check, which is not made in this case.

I reported the two problems related to scribe spell long ago, the first one was this, the second one was the missing check when the caster level was greater than or equal to the spell level. The 2nd seems to have been fixed since the Spring update, but I tested the 1st one and it hasn't been fixed.

I quoted the rule for spell scrolls in my first post (for ex, from Dungeons & Dragons 5th Edition System Reference Document documentation: https://dnd-srd-sphinx.readthedocs.io/en/latest/magic-item/spell-scroll.html), here it is in full: (the same text appears in other official documents, see ref below, it's simply easier to copy from there. Saying it's an independent website is not an acceptable rejection criterion)

Spell Scroll

Scroll, varies

A spell scroll bears the words of a single spell, written in a mystical cipher. If the spell is on your class’s spell list, you can use an action to read the scroll and cast its spell without having to provide any of the spell’s components. Otherwise, the scroll is unintelligible.

If the spell is on your class’s spell list but of a higher level than you can normally cast, you must make an ability check using your spellcasting ability to determine whether you cast it successfully. The DC equals 10 + the spell’s level. On a failed check, the spell disappears from the scroll with no other effect. Once the spell is cast, the words on the scroll fade, and the scroll itself crumbles to dust.

The level of the spell on the scroll determines the spell’s saving throw DC and attack bonus, as well as the scroll’s rarity, as shown in the Spell Scroll table.

Spell Scroll

Spell Level	Rarity	Save DC	Attack Bonus
Cantrip	Common	13	+5
1st	Common	13	+5
2nd	Uncommon	13	+5
3rd	Uncommon	15	+7
4th	Rare	15	+7
5th	Rare	17	+9
6th	Very rare	17	+9
7th	Very rare	18	+10
8th	Very rare	18	+10
9th	Legendary	19	+11

A wizard spell on a spell scroll can be copied just as spells in spellbooks can be copied. When a spell is copied from a scroll the copier must succeed on an Intelligence (Arcana) check with a DC equal to 10 + the spell’s level. If the check succeeds, the spell is successfully copied. Whether the check succeeds or fails, the spell scroll is destroyed.

So it still seems incorrectly implemented. As I understand it, the wizard must pass the DC check (and risk to lose the scroll on failure).

Some official references, in case this problem is tackled or added to the differences vs SRD 5.1.

- Systems Reference Document 5.1, rules of the Open Gaming Licence that are used in Solasta, pg 242, same text I copied above (document by WotC, available for download on their website) 

- DnD Basic Rules - the public document, simplified version of the Player's Handbook, pg 169-170, same text as above (document by WotC, available for download on their website)

- Dungeon Master's Guide, pg 200-201, same text as above (printed book by WotC, available for purchase in their store)

It was already like that in editions 3.5 and 3, though there are small differences in the procedures, mishaps, and so on.