Yes, there are specific frequency bands that 5G signal boosters currently cannot support. Current regulations limit signal boosters from amplifying many 5G bands[1]. The fastest 5G networks for AT&T, T-Mobile, and Verizon operate on bands n41, n77, n260, and n261, but consumer boosters do not reliably support these bands[2]. Most mid-band frequencies and all high-band frequencies are beyond the capability of current signal boosters[1]. In urban areas, 5G frequency bands are typically high-frequency, which are not supported by current boosters[9].
T-Mobile's 5G network operates on the 600 MHz band (n71) and the 2500 MHz band (n41), but FCC booster regulations are outdated and don't allow boosting on these bands[3]. Although the FCC has not yet issued blanket approval for boosters to amplify band 71 or band n77[6].
Citations:
[1] https://www.waveform.com/a/b/guides/5g-signal-booster-guide
[2] https://www.pcmag.com/picks/best-cell-phone-signal-boosters
[3] https://www.waveform.com/a/b/guides/tmobile-signal-boosters
[4] https://www.wilsonamplifiers.com/blog/5g-frequency-bands-explained/
[5] https://mysignalboosters.com/dk/product/5g-signal-booster-300-sqm/
[6] https://powerfulsignal.com/cellular-frequency-bands/
[7] https://mysignalboosters.com/cz/product/5g-signal-booster-300-sqm/
[8] https://www.signalboosters.com/blog/cellular-frequency-bands-a-simple-breakdown/
[9] https://www.lintratek.com/news/how-to-choose-a-5g-mobile-signal-booster-and-5g-antenna/