I have disabled my virus scanner (Windows Defender only) and the issues have not changed.

I'm currently experiencing a large number of issues trying to install games through the itch.io app while working through the Palestine and Ukraine bundles I purchased a while back.

Sometimes when attempting to install games, the app works as expected - it loads the install size of the file, it automatically selects a location, and it lets me install the game. I was able to queue multiple games/downloads at a time the first day I was using the app.

However, after a game or two, or sometimes even when opening the app for the first time, the performance is VERY slow.

I frequently get "JSON-RPC connection timed out". The app hangs when trying to click on install e.g. forever waiting on "computing space requirements". The app will not load additional rows of games (either no response or the same JSON error). And most importantly, 1 CPU core on an i5-10400F is pegged near 100% usage even when the app appears to be doing nothing (~13% total usage).  I have no idea what the app is trying to do and why it's maxing out a core to look like it's inactive.

For comparison, if I open firefox, I have 42 tabs of various itch.io pages open with ~5% usage of a single core, and I can download games directly from the downloads pages without issue.

One example error is below, but it doesn't really capture all of the issues:

I haven't found a solution. I haven't opened up the app in a while, but when I do I'll probably just play through my games top-to-bottom and uninstall each of them when I'm done.

I also have this same issue.  Closing out the app and reloading it works briefly but the timeouts quickly start occurring again.  It appears to be related to loading new entries in the Library view, which is necessary in order to scroll down to the games I haven't installed yet.

A "Not Installed" filter would be great to work around this, even if the core issue wasn't fixed.

Anything new about this? I#m not entirely sure yet what this is doing but I noticed it too.

I am also looking for a solution for this problem 

It seems like it would be an issue that the developers would like to prioritize, since it makes their app basically useless for anyone with any decently-sized library.  I'll also throw in that the app will take a noticeable amount of CPU even when seemingly idling, with no visible loading of anything or any indication that the app is doing anything at all.  I dare say that the app is badly written as it currently stands and that itch.io's continuing to keep the app as-is (and even their releasing it in its current state) shows that they just don't care.

In case this helps anyone..

A way to work around this is to install Playnite and install the itch.io plugin, and use Playnite to find your itch.io games, etc.  

If you want to install all itch.io games you don't have installed, then create a filter in Playnite filtering Library by itch.io and check the "Not installed" box.  Then, go down your list and double-click each entry you want to try.  That will pop up the install box in the itch.io app and you can install each item there one by one by one by one by one by one by one by one by ........  Note that a fair amount of the games, books, etc are somehow unable to be installed from the app but most of them work.

(Anyone looking at this has probably figured this out by now but..) If when trying to install something the itch.io app gives you an error something like "Too many HTPP connections", try again, because it means the app is hitting the itch.io website too quickly and the request will probably work if you try again.

Thanks @AstralUnicorn, I'll have to check out Playnite. I haven't thought about my itch library other than the last two justice bundles because I have thousands of games across other platforms but this could be a good way to keep track of what I already own.