This sort of mixed-case queries are 0x20 bit encoding and are a security measure for dns lookups, not a specific attack. The number and amount of queries may r

This sort of mixed-case queries are 0x20 bit encoding and are a security measure for dns lookups, not a specific attack. The number and amount of queries may rise to the level of being a DDoS and in that case you should consider options for serving your DNS ouside of your personal infrastructure like Cloudflare or Stackpath. To put it as clearly as possible, if you are on any sort of residential line and hosting all of your DNS there it is trivial for _any_ attacker to take you offline. You simply don't have access to the bandwidth necessary to deal with the attack and your ISP is not going to care enough to provide you with any real help. It is time to let professionals with access to real resources help.