Thanks user LilLillyFox on the LE Discord for digging up a fix.
Pre-season 2, LE ran decently well on my LCD Steam Deck. Depending on area and build I was getting between 40-60fps on medium graphics. CryoUtilities helped overcome the memory leak that plagued the first few patches. However, improvements to SteamOS and proton let me run LE well without the need for CryoUtilities and all was good for awhile.
Post-season 2 update, I began encouraging massive fps drops and lag, specifically in the new endgame weaver monos and cemeteries.
Tried reinstalling CryoUtilities but still had big frame drops. Switching proton versions did not help either.
The solution (perhaps only temporary) was suggested on Discord. It simply requires Steam Deck users to increase the UMA buffer size from the default 1GB to 4GB in the bios.
After doing that, I uninstalled CryoUtilities and set my proton back to experimental. Now I am able to play endgame monos with no issues.
I played for about 3 hours with no major issues or frame drops, so I would call this fix good enough to make the game playable. Hope this helps other Steam Deck users enjoy the new update.
Cheers!