You may be using an older php version. You have to change this with your hosting service or they should do the change. php 7.3 or php 7.4 is required for the new WebsiteX5 projects. Maybe it works with php 8.0, but you have to try it.

Thanks for your swift resonse. I just check the setting of one.com and it looks like be its running on version 7.4.3

See picture for more info. 

Is that what you meant?

It is possible that WebsiteX5 version 2020.3 is not yet compatible with php 7.4.3. Test if it works if you go back to php 7.3.

I will upgrade the software this weekend, let's hope that it will be fix.

Thanks for answers.

I did the upgrade and everything is good now.