Most of the diags roll over after 30 days - or they should. You can ensure they get removed:
https://learn.microsoft.com/en-us/answers/questions/50117/exchange-2019-logs-keep-growing.html
personally, I wouldnt keep more than that. If you are troubleshooting an issue, you arent really gonna care beyond 30 days IMO. Even then - you really would be looking at anything even more recent than 30 days.