It seems to me that VoLTE settting (with preffered network type LTE) is not working correctly since my laptop connected to this phones’s hotspot stop working when I’m in a call. It this known issue or it’s a bug?
I can’t comment on the hotspot disconnect, but I am fairly certain there are no issues with VoLTE on the device (I can confirm no issues for a Pixel 3a XL bonito at least).
You can check the VoLTE registration by dialing *#*#4636#*#* and then going to “Phone Information > 3 Dots > IMS Status”. If it isn’t enabled, then you are relying on 3G (or 2G if your area has shut down 3G towers already) which will certainly have degraded call quality.
I didn’t mean that the laptop disconnected from the hotspot, just that the internet stopped working when I was in a call That’s usually the sign that VoLTE is not active.
Before Iode, I had several other alternative roms (GraphemeOS, CalyxOS) with VoLTE on this phone.
Maybe contacting Carrier (Vodafone CZ) and letting them know it’s not working would help? The service (VoLTE) is active on their side, but maybe they don’t recognize this OS? Some IMS handshake problem?
IMS Status:
IMS Registration: Not Registered
Voice over LTE: Unavailable
Voice over WIFI: Unavailable
Video Calling: Unavailable
I recall in Switzerland it also didn’t work 
I would need to flash iodeOS again on it. I might give it a try just for proper reference.
Yes I think you need to check with them, but also it could simply be that your APN entry is not correct from “Settings > Network & Internet > SIMs > (your sim) > Access Point Names” so please check those. Upgrades from iodé v6 to v7 (due to upstream LineageOS changes) have caused some users to need to manually adjust those to suit their carrier.