How large are you opening the files? It's better provide some examples for troubleshooting.
Of course, you can try this snippet to check if it works.

(add-hook 'find-file-hook
  (lambda ()
    (when (too-long-file-p)
        ;; or (font-lock-mode -1)
         (fundamental-mode 1)
)))

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Meet the most at around 30M, occasionally at around 100M, and also at 1G or above

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Did you try the snippet above?

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Thank you , plus the above configuration to open a normal txt file, the speed has some changes, but if there is a 5000 lines or more python file, open the search operation still need to load a long time. For example, if you open a py file for the first time, and it contains a python dict formatted with 5000 lines, it will take a long time to load when searching.

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Since I don't have the examples for troubleshooting, I am wondering what about with emacs -Q. And it's better get profiling report to move forward. See profiling

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search:
176,526,018 68% + command-execute
70,353,849 27% + timer-event-handler
10,633,431 4% + redisplay_internal (C function)
211,344 0% winner-save-old-configurations
198,762 0% + substitute-command-keys
32,040 0% + sideline--post-command
17,840 0% + gcmh-register-idle-gc
16,830 0% + help-command-error-confusable-suggestions
12,328 0% + lsp-ui-sideline
12,160 0% + tooltip-show-help
10,258 0% + #<compiled -0x190659bcf02f3ea0>
8,288 0% + lsp--post-command
4,352 0% + corfu--auto-post-command
1,632 0% + #<compiled 0x181154b46c2ea924>
192 0% mouse--click-1-maybe-follows-link
184 0% global-hl-line-highlight
0 0% ...

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openfile:
56,517,802 50% + timer-event-handler
35,776,794 31% + redisplay_internal (C function)
14,742,696 13% + command-execute
5,326,711 4% + #<compiled 0x1da2b4d9e51249be>
190,784 0% + winner-save-old-configurations
151,666 0% + substitute-command-keys
45,213 0% + #<compiled -0x190659bcf02f3ea0>
37,788 0% + symbol-overlay-post-command
35,268 0% + sideline--post-command
32,406 0% xselect-convert-to-string
26,224 0% + gcmh-register-idle-gc
9,424 0% + lsp--post-command
8,368 0% + lsp-ui-sideline
8,184 0% + #<compiled 0x17d1feaf6e00be7d>
6,256 0% + jit-lock--antiblink-post-command
6,144 0% + corfu--auto-post-command
5,200 0% + eldoc-schedule-timer
5,181 0% + #<compiled 0x187939225f7e66fb>
4,144 0% + clear-transient-map
3,280 0% + tooltip-show-help
1,584 0% global-hl-line-highlight
1,056 0% + clear-transient-map
816 0% + gui-set-selection
320 0% mouse--click-1-maybe-follows-link
48 0% + deactivate-mark
0 0% ...

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Expand timer-event-handler and check the CPU percentages., please.

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search.zip
openfile.zip
I have exported the report for searching and exporting files to the attachment above. Thank you !

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`

data = {}

for i in range(6000):
key = f'key_{i}'
value = f'value_{i}'
data[key] = value

with open('large_dict_file.py', 'w') as file:
file.write('large_dict = ')
file.write(repr(data))
file.write('\n')
`
Alternatively, you can use the above code to generate a similar file and open it in python major mode, which may cause stuttering when opening and searching. Thank you !

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Thanks for the information! According to the reports, the bottleneck is highlight-indent-guides.

Please

1. Update to the latest version.
2. Try to disable highlight-indent-guides-mode`.
3. Evaluate (too-long-file-p).
4. Check the value of prog-mode-hook.

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The latest version has some effects. Thank you !

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