Interstellar travel isn't the issue — stars are close together and even at 10%c the Milky Way could be traversed safely in 10M years. 10M years isn't a factor. Even if it's 100x slower at 0.1%c, 1bn years to colonize an 11 or 12bn year old galaxy with 6-10bn year old metallic stars (thought to be required for life) isn't a strong filter.
If a filter parameter is the rarity of spacefaring civilization frequency, then even only one per galaxy or per 1000 galaxies isn't a limitation unless intergalactic (IG) dust density is high. (This still leaves 2bn civilizations in our visible universe.)
Need to hit 50%c to be able to send probes to a meaningful fraction of the visible universe before expansion takes them out of range. At a certain density level the redundancy factor (how many probes to send to ensure one arrives due to destruction in collisions with IG dust) becomes untenable and filters out IG travel or perhaps limits it to the local group due to Hubble constant increase.
Sharpening the Fermi paradox - intergalactic spreading has a discussion of the limiting factors due to IG dust density at specific masses/sizes and suggests another filter: IG policing of paperclip-maximizer accidents.