[Device]:

### Pre-flight checklist

- [x] I quit **Logi Options+** before testing.
- [x] I searched existing issues for my device.

### Device model

Marathon

### Connection

Unifying receiver

### What's the problem?

Device is detected but a feature doesn't work

### `openlogi list` output

```text
Unifying Receiver (3A119844, vid=046d pid=c52b)
└─ slot 1 ● M720 Triathlon (mouse, wpid=405e, battery=—)
```

### `openlogi diag features` output

```text
device: M720 Triathlon (slot 1 on receiver 3A119844)
idx id ver
0 0x0000 v1
1 0x0001 v1
2 0x0003 v2
3 0x0005 v0
4 0x1d4b v0
5 0x0020 v0
6 0x0007 v0
7 0x1000 v0
8 0x1814 v1
9 0x1815 v1
10 0x1b04 v3
11 0x1c00 v0
12 0x2205 v0
13 0x2100 v0
14 0x00c1 v0
15 0x00c2 v0
16 0x1803 v0
17 0x1806 v0
18 0x1805 v0
19 0x1813 v0
20 0x1830 v0
21 0x1861 v0
22 0x1890 v0
23 0x1891 v0
24 0x18a1 v0
25 0x1df3 v0
26 0x1e00 v0
27 0x1eb0 v0
28 0x18b1 v0
29 0x1850 v0
30 0x1f03 v0
31 0x18c0 v0
32 0x2121 v0
(33 feature entries)
```

### Details

The most important button is not recognized: the button that lies underneath the thumb.

Reproduce the report with the M720 Triathlon on a Unifying receiver, using `openlogi list` and `openlogi diag features` as the initial entry points. Identify how the thumb button is represented among the reported features and verify that the button is recognized and available for remapping.

Written by the indexing model from the issue text.