can someone assist me on how this works according to the rules? not really looking for the workarounds as I have ideas for that which I will post at the end.

so if a spell scroll has the cast of a 1 reaction but the rule for a scroll costs one action how do you use the scroll in combat. eg counterspell, Absorb elements.

the current workaround is that use you use an action to ready the spell and hold the reaction for the round. I can get them out of combat things like alarm casting of one minute even thou it's also more than an action 

Item description for spell scroll:

"Casting the spell by reading the scroll requires the spell’s normal casting time. "

If the spell is a reaction, like feather fall then you can use the scroll using your reaction casting the reaction spell from it. If the spell is a bonus action like Misty Step then you use your bonus action to use the scroll casting the bonus action spell from it.

In other words, casting a spell from a scroll is no different than casting a spell normally except it uses the stats of the spell scribed into the scroll not your own and you may be able to cast higher level spells through scrolls than your current class level allows and you don't need material components or spell slots. Basically a spell scroll is a way of casting a spell for free.

Any spellcaster with Arcana skill can make scrolls and it's not too expensive to make 1st level spell scrolls making it useful to use downtime to stock up on low-level spells you might use often like Mage Armor letting you save your spell slots.

I've never read where it says you can open a closed object and remove an item from it as 1/2 of a reaction...and then use the other 1/2 of your reaction to then cast a spell (which requires a full reaction).

If the scroll is already in your hand....sure, you can cast it as a reaction.

Quote from HeathSmith >>

I've never read where it says you can open a closed object and remove an item from it as 1/2 of a reaction...and then use the other 1/2 of your reaction to then cast a spell (which requires a full reaction).

If the scroll is already in your hand....sure, you can cast it as a reaction.

 
You replied to me directly so I am presuming you're directing this to me but I don't understand why since nobody is discussing scrolls being retrieved from bags. All we're saying is that spell scrolls can be cast as a reaction if the spell of that scroll has a reaction as a casting time. It's already assumed the character would have the readily available access to the scroll - since that is covered by other rules not being discussed here (and kinda obvious). 

Quote from HeathSmith >>

I've never read where it says you can open a closed object and remove an item from it as 1/2 of a reaction...and then use the other 1/2 of your reaction to then cast a spell (which requires a full reaction).

If the scroll is already in your hand....sure, you can cast it as a reaction.

Unless an object is stored in a bag of holding, grabbing it from a bag or pouch is either considered part of the action of using it (such as with ammunition) or a free object interaction (as with weapons). Neither interact with the casting time of the spell, and I believe that because a spell scroll is a consumable, pulling it out would be part of the action of casting it.

Either way, there's no 1/2 action business.

I I read on page 139 of the DMG that casting a spell from a spell scroll takes an action. It would be awesome to use something like shield with a spell scroll, but the RAW states "as an action". Here is the paragraph from the book:

Most scrolls are spells stored in written form, while a few bear unique incantations that produce potent wards. Whatever its contents, a scroll is a roll of paper, sometimes attached to wooden rods, and typically kept safe in a tube of ivory, jade, leather, metal, or wood. A scroll is a consumable magic item. Whatever the nature of the magic contained in a scroll, unleashing that magic requires using an action to read the scroll. When its magic has been invoked, the scroll can't be used again. Its words fade, or it crumbles into dust. Any creature that can understand a written language can read the arcane script on a scroll and attempt to activate it.

Misprint. Since errata'd.

Actual, up to date, text reads:

A scroll is a consumable magic item. Whatever the nature of the magic contained in a scroll, unleashing that magic requires the user to read the scroll. When its magic has been invoked, the scroll can’t be used again. Its words fade, or it crumbles into dust.

You'll note it doesn't say it takes an action anymore.

The correct ruling on actions for casting from a magic item are put further down.

Spells

Some magic items allow the user to cast a spell from the item, often by expending charges from it. The spell is cast at the lowest possible spell and caster level, doesn’t expend any of the user’s spell slots, and requires no components unless the item’s description says otherwise. The spell uses its normal casting time, range, and duration, and the user of the item must concentrate if the spell requires concentration. Many items, such as potions, bypass the casting of a spell and confer the spell’s effects with their usual duration. Certain items make exceptions to these rules, changing the casting time, duration, or other parts of a spell.

A magic item, such as certain staffs, may require you to use your own spellcasting ability when you cast a spell from the item. If you have more than one spellcasting ability, you choose which one to use with the item. If you don't have a spellcasting ability - perhaps you're a rogue with the Use Magic Device feature - your spellcasting ability modifier is +0 for the item, and your proficiency bonus does apply.

Reaction spell scrolls vis a vis object interaction time: My ruling (maybe I heard it somewhere) is that I assume a caster has a reaction scroll affixed to them in a way that allows for an almost immediate use (i.e. pinned to their cloak, fastened to the back of their arcane focus, etc.)  I also assume reaction scrolls take up less physical space (smaller) due to smaller casting time/fewer words etc, which allows convenient positioning. So far I haven't yet had a player abuse this with many Reaction scrolls; if they did I may ask them to tell me where each of them is and set a limit.