Have you tried to add DNS it might be because of your ISP or the DNS that blocking your Electrum from syncing?
Try to add DNS from your PC(ipv4 settings) put 8.8.8.8 and 8.8.4.4
Then test it again.
If you have an android phone you can try to test Electrum on your phone. If it still blocked from syncing the issue is under your network/ISP not the wallet itself.
in the similar old topic, I saw someone advised that exporting private keys into Coinomi wallet... Should I try it if it not have risks?
If you are going to use Coinomi wallet for desktop it will not be safe.
Like the above said much better to solve this issue rather than exporting it to Coinomi wallet but if you still want to export your seed to other wallets I recommend you to use the Electrum mobile instead.