EuroRust and CppCon are fantastic. If the budget is generous enough then I'd recommend mainstream ones like NDC, Devoxx, or Strange Loop.
Also, I've recently come across a newsletter that scans YouTube for newly uploaded conference talks and then sends them out in a weekly email. They maintain a list of conferences they're monitoring that is quite comprehensive. The newsletter is called Tech Talks Weekly and the conference list is here: https://techtalksweekly.substack.com/p/tech-conferences
Also, I've recently come across a newsletter that scans YouTube for newly uploaded conference talks and then sends them out in a weekly email. They maintain a list of conferences they're monitoring that is quite comprehensive. The newsletter is called Tech Talks Weekly and the conference list is here: https://techtalksweekly.substack.com/p/tech-conferences