You can define subfigures:

:::: {#fig:subfigures .figure .subfigures}
+:------------------:+:------------------:+:------------------:+
| :::: {#fi          | :::: {#fi          | :::: figure        |
| g:subfig1 .figure} | g:subfig2 .figure} | ![c](fig3.         |
| ![a](fig1.         | ![b](fig2.         | png){width="100%"} |
| png){width="100%"} | png){width="100%"} |                    |
|                    |                    | ::: caption        |
| ::: caption        | ::: caption        | c                  |
| a                  | b                  | :::                |
| :::                | :::                | ::::               |
| ::::               | ::::               |                    |
+--------------------+--------------------+--------------------+
| :::: {#fi          | :::: figure        | :::: {#fi          |
| g:subfig4 .figure} | ![e](fig5.         | g:subfig6 .figure} |
| ![d](fig4.         | png){width="100%"} | ![f](fig6.         |
| png){width="100%"} |                    | png){width="100%"} |
|                    | ::: caption        |                    |
| ::: caption        | e                  | ::: caption        |
| d                  | :::                | f                  |
| :::                | ::::               | :::                |
| ::::               |                    | ::::               |
+--------------------+--------------------+--------------------+
| :::: {#fi          | :::: figure        | :::: {#fi          |
| g:subfig7 .figure} | ![h](fig8.         | g:subfig9 .figure} |
| ![g](fig7.         | png){width="100%"} | ![i](fig9.         |
| png){width="100%"} |                    | png){width="100%"} |
|                    | ::: caption        |                    |
| ::: caption        | h                  | ::: caption        |
| g                  | :::                | i                  |
| :::                | ::::               | :::                |
| ::::               |                    | ::::               |
+--------------------+--------------------+--------------------+

::: caption
Figure 1: Caption. a --- 1, b --- 2, c --- 3, d --- 4, e --- 5, f --- 6,
g --- 7, h --- 8, i --- 9
:::
::::

:::: {#fig:subfigures2 .figure .subfigures}
+:--------------------------------------------------------------------:+
| ![a](fig1.png){#fig:subfig21}                                        |
+----------------------------------------------------------------------+
| ![b](fig2.png){#fig:subfig22}                                        |
+----------------------------------------------------------------------+
| ![c](fig3.png)                                                       |
+----------------------------------------------------------------------+
| ![d](fig4.png){#fig:subfig24}                                        |
+----------------------------------------------------------------------+
| ![e](fig5.png)                                                       |
+----------------------------------------------------------------------+
| ![f](fig6.png){#fig:subfig26}                                        |
+----------------------------------------------------------------------+
| ![g](fig7.png){#fig:subfig27}                                        |
+----------------------------------------------------------------------+
| ![h](fig8.png)                                                       |
+----------------------------------------------------------------------+
| ![i](fig9.png){#fig:subfig29}                                        |
+----------------------------------------------------------------------+

::: caption
Figure 2: Caption. a --- 1, b --- 2, c --- 3, d --- 4, e --- 5, f --- 6,
g --- 7, h --- 8, i --- 9
:::
::::

Figures themselves can be referenced fig. 2, as well as individual
subfigures: figs. 1 (a), 1 (b), 2 (i)