this is real strange. 

can you check if theme plugins were actually build and installed in cin_src_root/bin/plugins? 

for me it looks like

Report issues at https://termux.com/issues

$ cd cingg/cinelerra/cinelerra-5.1/

$ ls -la bin/plugins/

total 117

drwx------ 9 u0_a116 u0_a116 3488 Jul 25 11:56 .

drwx------ 14 u0_a116 u0_a116 3488 Jul 24 23:42 ..

drwx------ 2 u0_a116 u0_a116 3488 Jul 25 11:56 audio

drwx------ 2 u0_a116 u0_a116 4096 May 4 12:03 fonts

drwx------ 6 u0_a116 u0_a116 3488 Jun 29 17:32 picon

-rwx------ 1 u0_a116 u0_a116 38260 Jul 25 11:56 posterize.plugin

drwx------ 2 u0_a116 u0_a116 3488 May 4 12:03 scopes

drwx------ 2 u0_a116 u0_a116 3488 May 4 12:03 shapes

drwx------ 2 u0_a116 u0_a116 3488 Jul 25 11:56 themes

-rwx------ 1 u0_a116 u0_a116 38300 Jul 25 11:56 timelapsehelper.plugin

drwx------ 2 u0_a116 u0_a116 8192 Jul 25 11:56 video

$ ls -la bin/plugins/themes/

total 7495

drwx------ 2 u0_a116 u0_a116 3488 Jul 25 11:56 .

drwx------ 9 u0_a116 u0_a116 3488 Jul 25 11:56 ..

-rwx------ 1 u0_a116 u0_a116 646848 Jul 25 11:56 theme_blond.plugin

-rwx------ 1 u0_a116 u0_a116 1456700 Jul 25 11:56 theme_blond_cv.plugin

-rwx------ 1 u0_a116 u0_a116 648368 Jul 25 11:56 theme_blue.plugin

-rwx------ 1 u0_a116 u0_a116 736296 Jul 25 11:56 theme_blue_dot.plugin

-rwx------ 1 u0_a116 u0_a116 496464 Jul 25 11:56 theme_bright.plugin

-rwx------ 1 u0_a116 u0_a116 447052 Jul 25 11:56 theme_cakewalk.plugin

-rwx------ 1 u0_a116 u0_a116 651692 Jul 25 11:56 theme_hulk.plugin

-rwx------ 1 u0_a116 u0_a116 727340 Jul 25 11:56 theme_neophyte.plugin

-rwx------ 1 u0_a116 u0_a116 650624 Jul 25 11:56 theme_pinklady.plugin

-rwx------ 1 u0_a116 u0_a116 555616 Jul 25 11:56 theme_suv.plugin

-rwx------ 1 u0_a116 u0_a116 630696 Jul 25 11:56 theme_unflat.plugin

$