They can legally register a trademark (costs 500$ once and is done online).

After trade-marking competitors can still bid for your trademark but they can't write the trademark words in the title or content of the ads.

These two links explain how trademark vs ads works:

https://support.google.com/adspolicy/answer/6118?hl=en

https://www.brandverity.com/blog/google-ads-trademark-rules-...