The percentage setting in the Lyngdorf app changes how the amp shows its own volume. Roon shows the volume in dB for your amp, as your screenshot shows (-99.9 to 20 dB), and we are not aware of a setting in Roon that switches this to a percentage. Because the volume control in Roon is set to the amp’s volume, both show the same level in different units.
Thanks for the screenshots. We pulled the logs from your Roon Server and checked what the amp sends to Roon.
The TDAI-2210 reports its volume to Roon as dB, with a range of -99.9 to 20 in 0.1 steps. That is what Roon shows. The volume information the amp sends contains the type, the range, and the step, but not the display setting from the Lyngdorf app, so the Percentage option there does not reach Roon. The range your device reports is also visible in Roon under the zone’s volume limits, in the Device limits section:
Because Roon uses what the device reports, this can only change on the Lyngdorf side, in the amp’s Roon Ready firmware. Please contact Lyngdorf support and ask whether the TDAI-2210 can report its volume as a percentage to Roon. We cannot say what other Lyngdorf owners or other brands such as NAD see without knowing the exact model and firmware, since each device reports its volume in its own way.