"Advanced alien civilization colonizing our galaxy even just at 1% of the speed of light would have swarmed it in a few million years! So where are they????"

No, even just in-the-home-system colonization is extremely difficult and going outside is borderline impossible without warp magic.

Building, propelling, and guiding a gigantic spaceship with capabilities of
>self-sustaining
>resource-mining
>varieties-of-complex-chemical-manipulating
>self-parts-fabricating
>self-healing
>well-protected-against-small-object-impact (at least)
>self-improving
>gravity-generating-while-cruising
>sophisticated-medical-facility-harboring
>crew-gravity-difference-adjustment-enabling
>crew-reproduction-enabling

is such a pipedream for any civilization that can be reasonably expected to have emerged in a process somewhat similar to us, can manage to achieve on their home planets. With whatever super nuclear propulsion system they are using. We don't even know how many planets are even barely suitable for colonization within a few hundred lightyears. Let alone expecting they can eventually replicate their voyage that probably took their entire home planet's billions of citizen's decades to centuries worth of dedication.

Aliens, even if they are out there, are just living in their home systems and probably will all die there, just like we are very likely to be. Real space colonization is so fucking really fucking hard.
So almost all civilizations just end up making hyped youtube videos about doing it, and never actually do it. Let alone forming any sort of coherent bond with your colony people with centuries of communication delays. Fermi "paradox" solved. You just disillusion yourself from ridiculous space zoomer optimism in the premise and it's not even a paradox.