No : you can register a trademark in all countries.Trademarks are only limited to the territory they were registered in. And someone who owns multiple trademarks in different countries would already have that domain name in multiple tlds. Stop worrying about it and go ahead with your plans.
1- Have a look here -> https://www.wipo.int/reference/fr/branddb/1- Is there any way to find out if a domain has a trademark by someone?
2- What is the worst-case scenario if I start a website on the domain and it has a trademark by someone?
Read my comment again.No : you can register a trademark in all countries.
And someone who owns multiple trademarks in different countries would already have that domain name in multiple tlds
Sorry, I'm not awake.Read my comment again.