OUTLINE OPTION FOR THICK FONTS
[Starting with v9.39] Bubble Cloud has a new digital clock option Outlined ambient:
► Thick fonts are not normally recommended for always-on-display
► Enable this new option to prevent screen burn-in, and reduce battery use
► You can enable it for both single line and multi line digital clock
► Use the slider below to control the outline width
► The color of the outline will match the digit color you pick
► For single line digital time you can only set a single color

Outline font is applied automatically for these 8 themes:
→ bangers
→ aristocratic12 = mama (pack #4)
→ alien12 = flubber (pack #3)
→ sancreek (pack #2)
→ teko (pack #4)
→ mouc12 (pack #10)
→ default (Roboto narrow)
(off by default for others)

Most watches use OLED screen technology, which consume less power if fewer pixels are lit. Outline fonts combined with outline icon packs such as the Color Lines icon pack, you can further reduce the power use of your watch face: