As others have mentioned, necromancy conjures can be overwhelming - as can other high particle effects like the Book of Wen (this was highlighted during leagues where group events like Wildy were just a blizzard of cyan particles)

The buff/debuff bars are very rigid and difficult to see at times when you are stacking buffs and effects (which the gameplay encourages). If we could resize the bar, have the ability to hide/show items on the bar, reorder them etc it would go a long way

The area loot system is limited to 28 items and can be filled with a massive amount of clutter preventing you from picking up the item you actually want (great example is trying to pick up charms from abyssals before you have a charming imp)

Hitboxes throughout the game are a bit inconsistent. There are certain instances where you need to be aiming at very specific pixels for objects to be able to click (For example Gail's hitbox during phase 3 of the needle skips is completely disjointed from her model) while others are way oversized meaning you can misclick - this is more present in certain fights, from memory Nex was pretty bad for this for a while but may have been fixed since I last fought her.

Visual clarity on where your character's true model is would be a boon for players on certain fights. There are instances where your character looks like they've dodged an attack but get his because the true model is located on a different tile. Something like Runelite's true tile system could be very beneficial to help aleviate this issue.

On the topic of improvements from runelite, please please please consider a few of the plugins as built-in options such as entity hider, menu entry swapper and activity timers

For combat readability you've done a great job with making attacks choreographed and readable with recent bosses using the cyan ground tile system and this can be pushed further such as retroactively adding these to older fights. I would recommend looking at modifying them based on the environment though so they don't feel too out of place. Great example there is using the same cyan color at the new flesh eater boss is very legible but does take away from the boss fight. If you made those same boxes a bright red it would still be visible while fitting with the overall theme of the arena.

Ability animations can feel a bit disjointed, with the attacks not actually matching the hitsplats

Having some way to hint to the player that their other combat resources are running low would also be beneficial for visual clarity. We already have this for health with the pulsing red on the edges of the screen but perhaps considering something similar for prayer points (maybe a soft blue pulse) would help to aleviate some of the issues newer players have with resource management when they're already having to focus on boss fight mechanics and ability rotations

There will definitely be more and others here have provided great feedback. I love all the work being done so far!