@Ankacat What CPU cooler did you end up using? Did you have any concerns about putting strain on the motherboard when traveling with your computer?
The OP will have to confirm, but from looking at the pictures, that's a Cryorig C7. It's a low-profile, small cooler rated for a maximum cooling capacity of 95W, which means that there's essentially zero chance of it damaging anything (low weight+center of gravity close to the motherboard), but it'll also throttle your 9900K quite heavily (a stock 9900K, despite its 95W on-paper TDP, pulls 150-170W or more under short-term turbo, and 120-130 long-term if the cooling allows, though this depends on motherboard/BIOS settings). It's likely safer than the NH-U9s you seem to have decided on for your build, but that is also a relatively small and lightweight tower cooler, so I wouldn't be overly worried. Just handle your PC with care, and don't jostle it in any dramatic way, and you're likely to be fine. Carrying it in a padded bag of some sort ought to alleviate most concerns. The 9900K is a very power-hungry CPU (no wonder - it's an 8c16t CPU with very high turbo clocks), so it needs beefy cooling. You could use a C7 if you wanted, but you'd be leaving
a lot of performance on the table. The CU (copper) version of the C7 will be somewhat better, and even more if you replace the stock fan with a more powerful 25mm-thick fan (there are 3D-printable fan brackets for this available on the forums), but it still won't come close to the cooling capabilities of the U9s.