In https://github.com/elastic/elasticsearch/pull/88639 we introduced a new setting that allows configuring a maximum headroom in disk watermarks that helps reducing the waste of disk space in large disks. The disk health indicator should take that new setting into account to avoid reporting issues when there's still room for new data in the cluster. 

https://github.com/elastic/elasticsearch/blob/6ec31ed1533e6aaf8fc6dabda5e419f5dce984fa/server/src/main/java/org/elasticsearch/health/metadata/HealthMetadata.java#L193-L199

Those calls should take into account the available max headroom.
server/src/main/java/org/elasticsearch/health/metadata/HealthMetadata.java
in.readString(),
                FLOOD_STAGE_WATERMARK_FIELD.getPreferredName()
            );
            RelativeByteSizeValue frozenFloodStageWatermark = RelativeByteSizeValue.parseRelativeByteSizeValue(
                in.readString(),
                FROZEN_FLOOD_STAGE_WATERMARK_FIELD.getPreferredName()
            );
            ByteSizeValue frozenFloodStageMaxHeadroom = ByteSizeValue.readFrom(in);
            ByteSizeValue highMaxHeadroom = in.getVersion().onOrAfter(VERSION_SUPPORTING_HEADROOM_FIELDS)
                ? ByteSizeValue.readFrom(in)
                : ByteSizeValue.MINUS_ONE;
            ByteSizeValue floodStageMaxHeadroom = in.getVersion().onOrAfter(VERSION_SUPPORTING_HEADROOM_FIELDS)
                ? ByteSizeValue.readFrom(in)
                : ByteSizeValue.MINUS_ONE;
            return new Disk(
                highWatermark,
                highMaxHeadroom,
                floodStageWatermark,
                floodStageMaxHeadroom,
                frozenFloodStageWatermark,
                frozenFloodStageMaxHeadroom
            );
        }
        @Override
        public void writeTo(StreamOutput out) throws IOException {
            out.writeString(describeHighWatermark());
            out.writeString(describeFloodStageWatermark());
            out.writeString(describeFrozenFloodStageWatermark());
            frozenFloodStageMaxHeadroom.writeTo(out);
            if (out.getVersion().onOrAfter(VERSION_SUPPORTING_HEADROOM_FIELDS)) {