Hi @WhonixTa
Glad to here you resolved your issue. As it turns out what I mentioned earlier is no longer an issue as Electrum does not require Apt-Pinning when installing.
If increasing RAM and cpu cores fixed the issue then the it was it was not enough RAM/cores allocated.
You should not be using anything other than TBB with Whonix. Reasons:
https://whonix.org/wiki/Tor_Browser
You can have unexpected results if you use Firefox instead of TBB. This thread gives an example:
https://forums.whonix.org/t/google-calculated-me-across-whonix/4087